The rear main seal was leaking on our 2007 Suburban 1500 4wd. I did not want to tackle that one myself, as it was a bit more of a chore than I wanted to take on. A local mechanic replaced the rear main seal and the oil pan gasket, and when we picked it up to drive it home, the transmission wasn't working. When we got it up to freeway speeds, it just went out, like it was pushed into neutral or something. We pulled over and sat on the side of the freeway for a minute and we were able to go again. We got it up to about 45mph and it went out again. As we were coasting up the off-ramp, we felt it pop back into gear. We contacted the mechanic and took it back to him. He is a great guy, and is standing by his work. I am hoping he will get it back into working order. I am just curious as to what it could possibly be? I know the transmission and transfer case had to be pulled back to access the rear main seal. Could something have been broken or put back in out of alignment for the transmission to have stopped working like that? I am baffled (and I openly admit my lack of knowledge on this part of my vehicle).

Any leads would be appreciated!

Hope everyone has a safe and happy Turkey Day!

 

The obvious is still out there. Fluid level and condition and he will just recheck his work.

 

Maybe the shift linkage isn't properly installed.

 

I'm currently having the same problem, I replaced my rear main seal and transmission won't shift into third gear, stops around 45 mph

 

Has anyone found what caused this problem?
I am experiencing this same issue.