The Allison transmission in a Chevy 2500HD diesel depends heavily on the model year. Chevy has used several different Allison models over the years. To know for sure, you need to check the
build date and possibly the VIN of the specific truck.
There's no single answer. You'll find different Allison 1000 series transmissions (like the 10L1000) in various model years. Later models might have different versions within that family, or even a completely different Allison transmission.
