Trans slipping between 2nd & 3rd

[77 casa grande]

I have a th350 thats slips when shifting from 2nd to 3rd on hard accelerations but will shift when I back off, and it shifts smoothly on lite acceleration. Also noticed it never happens when its cold, only after everything warms up.

I had no issues with my trans prior to an engine swap I did last spring. At that time I drained as much fluid out of the body and converter as possible and refilled with synthetic fluid.

Could it be the
A) the fluid? Too thin and not gripping the plates
B) modulator? not shifting at lower vaccume pressure
C) just coincidence? and I'm just due for a rebuild.

 

[diesel4me]

Could be your detent cable is not adjusted properly,or the modulator might not be hooked to the correct manifold vacuum source or its diaphram is failing...I dount the fluid change had anything to do with it,but who knows...

 

[ion]

sounds like it's time for a rebuild. But if you keep the th350 invest in the biggest cooler you can and preferably one with a fan built into it. or swap in a manual tranny and not have this problem. That's what I did.