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Transmission overheating while pulling heavy loads Silverado Diesel 2500 HD Duramax

While pulling a four horse trailer (loaded with four horses) the automatic Allison transmission of our 2005 Silverado 2500 HD diesel truck heats up while driving in a mountainous or hilly area. We have to apply several techniques to keep the temperature down: stopping until the temperature goes down, using the manual gears, preventing the gear from going into overdrive, Does anyone know whether this is normal or should we send it into repair and can it be repaired? Thanks and regards.

You might look into having a secondary transmission cooler installed, always recommended for trailer towing…Locking out the overdrive is also standard procedure for heavy load towing, especially in the mountains…

What alerts you to the overheat condition? A warning light or transmission temperature gauge?

Have you been servicing the transmission on a regular basis, and I mean every 25-30k miles?? Allisons are very expensive units to build so you REALLY NEED to be servicing it on a regular basis especially because you tow. With that said, your truck should have come with a extended transmission cooler. You can upgrade the extended cooler with a heavy duty one. There are coolers which come with cooling fans attached for approx $170-$225. Well worth it on the Allison.


Thank you very much for this advice. I will contact the transmission dealer immediately for a heavy duty cooler.
Kind regards.

While you are at it you might want to have the trans serviced. And I mean a COMPLETE service with the pan dropped and the filters changed, NOT just flushed. Also to be safe, have the shop flow test the current coolers to make sure you dont have a restriction somewhere.