I have a th350 in a 92 chevy truck that won't shift into drive once it warms up. It shifts fine when engine is cold but once it warms up I have to shift it into neutral before it will go into drive. Then when its in drive it wants to downshift into second. I've got the vacum tied directly into the manifold. I've had it in truck for 4 months and it worked fine. Any suggestions much appreciated?

THANK'S IN ADVANCE...

 

Bad direct clutch lip seal

Needs a rebuild