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Allison 1000 Transmission Spotlight

Allison 1000

The Allison 1000 is a 6-speed double overdrive transmission produced by the Allison Transmission Company in Indianapolis, IN, and Baltimore, MD. Allison transmissions have a global reputation for being extremely durable, which is why they’re cheaper to operate than other equally equipped vehicles. The low minimum maintenance requirements result in cheaper overall maintenance costs.

This heavy duty transmission can be found in all sorts of motorhomes and custom applications, along with the Chevrolet Silverado, the Hummer H1, the Chevrolet B-Series and the GMC Sierra. It can also be found in the Chevrolet Kodiak and the GMC Topkick. Starting in 2001, Chevy 2500 HD and 3500 trucks have had the option of being equipped with the Allison transmission. The Duramax-powered engine in the Silverado 2500 and 3500 trucks are now combined with the Allison 1000.

The Allison 1000 is an extremely heavy duty transmission, capable of handling up to 620 lb-ft of torque. Compare this to GM’s highest-rated transmission, the 4L80E which can only handle 420 lb-ft of torque. Put into use in 2006, the Allison 1000 transmission is still in production.

Early Allison 1000’s were initially 5-speed transmissions, but in 2006 they added a sixth overdrive gear. The creators of the Allison transmission realized that the diesel engines offered in diesel pickups were constantly increasing in horsepower and torque. The creators of the Allison transmission realized that the diesel engines offered in diesel pickups were constantly increasing in horsepower and torque. They knew that a strong transmission would be needed to handle GMC’s Duramax engine.


The adaptive learning technology provides a comfortable driving experience and helps you avoid any rough shifting experiences. The Allison 1000 is completely electronically controlled to adapt to your current driving style. The computer in the Allison 1000 constantly adjusts shift clutch pressure to match engine torque and vehicle load. The computer also has pre-programmed tables for reference. It attempts to make the shifts match the programmed table to maximize durability and drivability.

Most commonly, the transmission may go into “Limp Mode” during the 4 to 5 upshift or between 5 to 4 downshift while under hard acceleration. This will cause a check engine light to come up on your dash and the truck to be limited by power and speed. When this happens, the most common reported code is P0700. GM defines P0700 as “Transmission Control Module Requested MIL Illumination”. Simply put, it’s a general code for transmission issues and generally is accompanied by another code such as P0701, P0702 or others.  

Many truck owners’ first reaction is to replace the Transmission Control Module (TCM) as soon as this code pops up. The reality is that further diagnosis is needed to tell what the issue is for sure, and the best way to resolve it. Never jump to conclusions with your transmission, and always take into consideration the circumstances behind the issue prior to the code coming up if you experience any problems.