Trans issue

[Sierra946]

I have a 99' limited, 3.4, auto trans. I had the front torque converter seal go on trans. So I dropped the trans and replaced the seal. While I had the trans down, I replaced rear main while I had trans dropped. 2 days later I did valve cover gaskets. The problem:
Now once I get into 3rd gear after car warms up, the trans revs like its in neutral if I give it any more than 25% throttle.
I've tried adjusting the lockdown cable , doesn't help. Any ideas?

 

[vm_boy]

Have you checked the ATF?

 

[Sierra946]

Yes. Level is where it's supposed to be. If it was low it would be slipping all the time, not just 3rd and fourth.

 

[Sierra946]

Now I'm getting a shudder in 1st and 2nd and the slippage in 3rd and 4th.

 

[Robb235]

Check engine lights?