I have a strange problem. On Sunday, my 2001 Yukon XL (5.3) started revving real high between 2nd and 3rd gears. Then a loud sound like marbles was heard from underneath. Anyways, it got worse until I could not get reverse. I let it sit for 2 days and this evening, it started fine and ran fine for a short time. Then the sounds started again so I let it sit. I am thinking that it might be the transmission, but why would it act fine for abiout 5 minutes then start back to running bad again?:banghead:

I you are loosing reverse and the fluid is full, this an internal trans problem.

Time to get a GM reman or new with a nice new warranty.

I did that.