I posted in another thread, but here's a new diagnostic clue. If the truck sits overnight it shifts fine. When it gets warm in drive I go to neutral when it shifts into fourth. OD band and servo are fine. Servo clip is intact. But... If it's warm and I manually shift from 1-2-D then it shifts into OD. Go figure. What do y'all think is going on?

 

When is the last time the fluid and filter were changed?

 

Tranny was rebuilt a year ago. Less than 8000 miles on it. I went ahead and changed fluid and filter two weeks ago when I pulled valve body to look at OD servo and OD band. I pulled servo inspected the seal, and pushed the OD band to see if it was broke. Lined everything back up and changed 2-3 spring back to OEM instead of heavy duty that was put in at rebuild. Sonnax cure kit was used during rebuild. Borg Warner clutches were used and heavy duty OD and reverse bands were used. I'm still thinking valve body is going bad. Since it only does it when it's warmed up still makes me think fluid is bypassing valves and not building pressure.