The Allison 10L1000 10-speed transmission is the heavy-duty automatic for Chevy Silverado and GMC Sierra HD trucks. That means it is a stout, though complex transmission, able to take the added burden the Duramax diesel engine puts out. It has the highest relative torque capacity of any full-size truck made. But problems have cropped up which we’ll cover now.

GM debuted the 10L1000 transmission in 2020 pickups. It replaced the Allison 1000 and 2000 six-speed automatic in 2001 to 2019 GM Duramax trucks. Ford and GM jointly developed the 10-speed. Internally, the 10L1000 and Ford’s TorqShift 10R140 are almost identical. Parts are interchangeable between the two.

Most of these problems occur due to aftermarket applications. Many heavy-duty truck owners prefer tuning changes or larger tire sizes to personalize and beef up their GM heavy-duty trucks. That is when many of these issues will pop up. 

Silverado and Sierra HD automatic torque converter weaknesses

The main issue plaguing the Allison 10-speed is the torque converter, according to NextGen Diesel. Or more specifically, the lockup mechanism. Ford’s version, which has proven superior, has a lockup mechanism that faces the stator. Conversely, GM’s version has it facing the flexplate. 

There’s a fine line for the transmissions where when everything is kept stock, it performs properly. Everything works fine until power levels exceed the 500 hp factory numbers. That or increasing tire sizes. Then, transmission failure is usually the result. 

In the case of tire size, the rear end gears need to be replaced to coincide with factory ratios. With aftermarket power increases, you should go with a billet multi-friction torque converter that can handle the extra output. 

The inferior stator in the Silverado and Sierra HD transmission

The stator controls stall speed and is located inside the torque converter. Stall speed is the speed at which the torque converter limits engine speeds. It limits the power transferred to the transmission. But it can also raise temperatures in the transmission. Heat management issues can be a problem for heavy-duty Allison automatic transmissions even since the earlier 1000/2000 six-speed automatics.

Since the stator is inside of the converter, replacing the entire torque converter with a stronger aftermarket version normally increases the reliability of the 10L1000. Prices range from around $1,000 and up. Replacing the torque converter is a fairly simple process as long as you have a lift. Otherwise, it would be best to have it replaced professionally.

Allison 10L1000 oil pan leaks

As with many components made from thin sheet metal or plastic, heat and use take their toll on the transmission pan. When this happens, the thin metal can deform and cause leaks to appear. It happens with many transmission and oil pans, and also valve covers. Aftermarket transmission pans are usually made from thicker or reinforced aluminum or steel, eliminating warping from heat/cold cycles. These aftermarket pans normally run around $300 and are deeper, to increase oil capacity, too.