Quote:
Originally Posted by bsmith0404
In 2012, GM only offered one rear end gear in the 2500 suburban. Off the top of my head I don’t know what it is, but if you check inside the glove box there should be a label that has a bunch of 3 digit codes. Normally around the center or label is a GU code. Typically GU4, GU6 or GU8. You can google that code to see what your rear gear is, but I believe they are 3:08, 3:55, and 3:73 respectively.
As for trans temps. The owners manual will typically give you a normal range. I think you’ll find 160 is normal warm temps. When towing heavy through mountains you will typically see trans temps around the same area as your coolant temps since the radiator is used for cooling trans fluid as well. As others have mentioned, I believe anything under 200 is fine. Short runs over a mountain pass above 200 is ok as well as long as it cools back down when the work load is reduced. I would get concerned if it jumped over 220-230 range or if it stayed in that range for extended periods even when work load is reduced such as going down the other side of a hill climb or running on flat.
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I wish I could have said it this completely and succinctly.