2001 GMC Sierra 2500 HD Q&A
2001 GMC Sierra 2500 HD Question: does the 3500 have the same rear end?
The differential will bolt up under your 2500. The tag on the differential should tell you what the gear ratio is. If the tag is missing you can either count the ring gears or count how many times you turn the pinion to get 1 revolution of an axle shaft. - Chevy Power