Ive got an '85 Z28 with the 700r4. This morning I drove about 20 miles with no issues, I then parked the car for a few hours then drive across the street and shut if off. After only a few mins I get back in and the car wouldnt shift out of first until about 3-3500rpm and it was a pretty hard jerk when it finally did. Several hours later I get back in and drive another 20 miles back to post with the car not shifting until 3-3500 rpm. I shut it off and just a few mins later get back in and the car was back to normal shifting at the normal times.
I plan on changing my fluid/filter asap. Any idea as to what could be the problem?

 

well i have recently had this problem with my 86 camaro and it was a combination of a broken governor gear and a stuck/worn valve in the valve body. the repairs cost $ 200. and the shop didnt even have to remove the trans to repair it. now all is well .SO this is where id start if i was you. hope this helps you out