I have a 97' D1, I just had the head gaskets replaced a second time in 2 years NOW my transmission takes a while to warm up and work properly. It wont shift out of it's lower gear when cold. It just rev's up and when it gets warm, then works pretty good. I have not had this issue before the head gasket replaced and have not been towing anything. 144,000 miles. "Pretty Good" means it changes gears somewhat like it did before the head gasket repair. BUT, it does hard shift occasionally (clunk). IDEAS????

 

What does the fluid look like?

 

It is not a beautiful red like new fluid by no means. I have actually drained a fair amount of fluid and replaced it with new fluid twice not too long ago. To answer your question Brownish Black

 

The color is likely shown on a clean paper towel as dark particles, usually clutch dust. New fluid and filter will help, but DIY you can't get all the fluid out of the torque converter, and you end up making several fluid changes in short miles. The tranny works on pressure, and if you put in a container of Lucas transmission fix that will boost pressure and improve shifting.

 

a common problem after having the heads off is not having the kick down cable routed correctly,
that would cause these issues, make sure it is hooked up properly on both ends and that is is run in a smooth curve down to the tranny and not caught up on somthing