2008 hummer h3 engine change

[jimmy]

I recently replaced my engine in my 2008 hummer h3 3.7L. For some reason my transmission is now messing up first and second gear shift fine. When going into 3rd gear my RPMS shoot up to 6000 before shifting and then will not shift into overdrive, have I missed something ? had no transmission issues before engine trouble

 

[mjferencak]

What was the reason(s) for the engine replacement? Your engine symptoms may lead to a trans replacement also but just from what you've said so far it sounds like the trans was the next weak link in the chain. Might be a bad torque converter. I know when my trans S'd the bed it would shift to 3rd and rev up as if it was in neutral. I knew then I had bad clutches.

 

[deserth3]

Did you do the work yourself? Most likely it was something done during the change.
Does your check engine light come on?
Did you remove the fuse/relay box?
Some of my recent tranny problems were treated to corrosion underneath.

Sent from my Moto G (4) using Tapatalk

 

[CaseyS]

Sounds like 3-4 clutches gone in the trans. Those are applied in 3rd and 4th. It may be shifting to 4 just slips as bad or worse than 3rd. Sounds like a rebuild is in order.