Duramax Buyer's Guide: How to Pick the Best GM Diesel

Chevy runs deep and Duramax-powered GMs with Allison transmissions behind them run even deeper! All in all, ¾- and 1-ton Chevy Silverados and GMC Sierras offer what are arguably the best all-around heavy duty trucks produced by the big three. Whether you’re after horsepower and torque, fuel economy, ride comfort or reliability, the Duramax-equipped rigs coming out of Detroit over the past decade and a half are tough to beat.

001 2015 duramax allison gm

Fair warning, these trucks generally hold their value better than Ford and even Dodge trucks of the same vintage, and the pre-emissions versions (2001 to 2007) are highly sought after. So, keep in mind that you may have to fork over $20,000 or more for an immaculate, 10-to-12-year-old truck.

2001-2004 2500 & 3500

002 2003 gmc sierra 2500 duramax

While the first models of GM trucks to offer the Duramax engine/Allison transmission combo are aging, clean versions can still command a pretty penny. The one Achilles heel of the LB7 Duramax engine is injector failure. Sooner or later, the injectors will need to be replaced (a $3,000 to $4,000 expense depending on the shop performing the work). However, once the injector issue is addressed, the LB7 is extremely reliable. The lightweight and independent front suspension on these trucks makes obtaining 20-mpg a cinch and gives them better ride comfort than their solid front axle Ford and Dodge counterparts.

Engine: 6.6L LB7 Duramax V8 with Bosch common-rail injection system

Transmission(s): Allison 5-speed automatic, ZF-6 6-speed manual

Best Year(s): Any year, as long as all 8 injectors have been replaced with genuine Bosch re-man units

Price Range: $7,000 to $15,000 

Pros:

  • Common-rail injection
  • Quiet operation
  • 450 hp is possible with a hot programmer
  • Excellent ride comfort thanks to an IFS suspension
  • Commercial-grade Allison A1000 automatic transmission option

Cons:

  • Injector failure is a guaranteed
  • Allison automatic will not handle more than an additional 90 hp for long
  • Flexing tie rods are a concern when off-roading, drag racing or sled pulling in 4x4
  • No factory lift pump
  • Heavy trailers push these trucks around more than Ford or Dodge models
  • Rocker panels and cab corners rust at accelerated rates in northern regions (salt, humidity)

2004.5-2005.5 2500 & 3500

003 2005 chevy silverado 2500 hd

As far as powertrain, suspension, and chassis is concerned, few changes exist between LB7 equipped GM’s and the ’04.5-’05.5 LLY Duramax-powered trucks. However, LLY engines do not have the same injector issues as the LB7 (and the LLY’s injectors are accessible without pulling the valve covers). Instead, this generation Duramax is known for overheating issues, namely when towing heavy. In addition, high-mile versions are prone to popping head gaskets. On the plus side, the LLY featured the largest turbo offered on any Duramax engine, and it utilizes variable geometry technology for optimum spool up, mid-range and top-end power. 

Engine: 6.6L LLY Duramax V8 with Bosch common-rail injection system

Transmission(s): Allison 5-speed automatic, ZF-6 6-speed manual

Best Year(s): Any year — just be prepared for the possibility of replacing the head gaskets and facing overheating issues if you plan to tow heavy.

Price Range: $10,000 to $19,000

Pros:

  • Common-rail injection
  • Quiet operation
  • Variable geometry turbocharger
  • 450 hp is possible with a hot programmer
  • Good ride comfort with IFS suspension
  • Commercial grade Allison A1000 automatic transmission option

Cons:

  • Overheating issues are common on the LLY engine
  • Blown head gaskets are more common on the LLY engine
  • Allison automatic will not handle more than an additional 90 hp for long
  • Flexing tie rods are a concern when off-roading, drag racing or sled pulling in 4x4
  • No factory lift pump
  • Heavy trailers push these trucks around more than Ford or Dodge models
  • Rocker panels and cab corners rust at accelerated rates in northern regions (salt, humidity)

2006-2007 2500 & 3500

004 2006 gmc sierra 2500 hd lbz

Perhaps the most desired of all Duramax models are the ’06-’07 Classic body style trucks. With arguably the best plug-and-play horsepower potential (on top of 360 horsepower being offered right out of the box), the last of the (essentially*) emissions-free engines, and a stronger, six-speed Allison to back them, the LBZ Duramax has a lot going for it. These trucks still incorporate the ride-friendly IFS, quiet and proven Bosch common-rail injection system, and are very reliable. However, all of the above makes for a hefty price tag on most models. Unless you find a deal, expect to pay 20K (or more) for a low-mile, excellent condition version. 

Engine: 6.6L LBZ Duramax V8 with Bosch common-rail injection system

Transmission(s): Allison 6-speed automatic, ZF-6 6-speed manual (‘06)

Best Year(s): Either year

Price Range: $14,000 to $25,000

* Exhaust gas recirculation (EGR) was used on ’06-’07 trucks (as well as the ’04.5-’05.5 LLY), but the diesel particulate filter and diesel oxidation catalyst had not debuted yet.

Pros:

  • Common-rail injection
  • Quiet operation
  • 6-speed Allison A1000 automatic offered
  • 450 hp is possible with a hot programmer
  • Good ride comfort with IFS suspension 

Cons:

  • Allison automatic will not handle more than an additional 120 hp for long
  • Flexing tie rods are a concern when off-roading, drag racing, or sled pulling in 4x4
  • No factory lift pump
  • Heavy trailers push these trucks around more than Ford or Dodge models
  • Rocker panels and cab corners rust at accelerated rates in northern regions (salt, humidity)
  • Cracked piston issues surface at higher horsepower levels

2007.5-2010 2500 & 3500

005 2009 chevy silverado 2500 hd lmm duramax

A brand new body style, vastly improved interior, and a fresh version of the Duramax graced the ’07.5 to ’10 model year 2500 HD and 3500 trucks. In order to meet tougher emissions standards, the LMM Duramax would be the first 6.6L to dawn a diesel particulate filter, diesel oxidation catalyst and more extensive EGR system. Because the exhaust after-treatment process requires fuel to function, mileage numbers are lower starting with the GMT900 generation. Other than that, the LMM engine itself remained very similar (hard-part wise) to the LBZ that preceded it — meaning performance potential is just as good.

Engine: 6.6L LMM Duramax V8 with Bosch common-rail injection system

Transmission(s): Allison 6-speed automatic

Best Year(s): Any year

Price Range: $14,000 to $35,000 

Pros:

  • Stronger version of the Allison A1000 automatic
  • Updated body style and interior
  • 450 to 500 hp is possible with a hot programmer
  • Good ride comfort with IFS suspension

Cons:

  • Diesel particulate filter/exhaust after-treatment system adds a failure point
  • Lower fuel economy than previous models
  • Weak tie rods are a concern when off-roading, drag racing or sled pulling in 4x4
  • No factory lift pump
  • Cracked piston issues surface at higher horsepower levels

2011-2016 2500 & 3500

006 2011 gmc sierra 2500 hd lml duramax

Thanks to a fully boxed frame, beefier independent front suspension, and an asymmetrical leaf spring design (with wider leaf springs to boot), the 2011 to 2016 trucks are the most capable tow-rigs GM has ever produced. As for the LML Duramax under the hood, its internals remain similar to what was found in LBZ and LMM mills. On the emissions side, it goes a step beyond what you’ll find on the LMM ’07.5-’10 trucks with the addition of diesel exhaust fluid (also known as urea injection). Subtle to major issues surface thanks to the added complexity of the emissions-controls and after-treatment system, and a different injection pump (used to meet more stringent emissions standards) leads to less plug-and-play horsepower potential than previous models.

Engine: 6.6L LML Duramax V8 with Bosch common-rail injection system

Transmission(s): Allison 6-speed automatic

Best Year(s): ’13-later (most costly injection pump failures seem to occur on ’11-’12 models)

Price Range: $25,000 to $70,000

Pros:

  • Fully boxed frame
  • Upgraded, stronger IFS
  • Improved rear suspension with asymmetrical leaf spring design
  • Stronger version of the Allison A1000 automatic
  • 450+ hp is possible with a hot programmer
  • Improved towing manners over ’01-’10 trucks
  • Integrated exhaust brake
  • Integrated trailer brake controller

Cons:

  • Diesel particulate filter/exhaust after-treatment system adds a failure point
  • Weak tie rods are a concern when off-roading, drag racing or sled pulling in 4x4
  • No factory lift pump
  • Limited aftermarket power potential due to factory CP4 injection pump

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