Ok so my 91 Ta shifts fine from a dead stop to 4th gear but its when im in town where I have some problems. If I am not below 20 miles per hour and I push the accelerator, the transmission shifts into 3rd gear for like one second and then immediately shifts to 4th and my rpms drop to 950. So to combat the problem, I have been just driving in second gear while in town. Any ideas on what this would be? My guess would be towards the torque converter.

-Transmission fluid changed and helped a little about 1,000 miles ago. I also adjusted the shift linkage (the one by the throttle cable). It drives just fine but It just bothers me not knowing what would cause that. 74,000 miles on car. Odd thing is that when I first pull out of the driveway, It will shift perfectly just at the right rpms from 3rd to 4th, but it only does it once before it starts shifting funny. If it is the torque converter, what kind of money are we talking and have to pull tranny to replace it?

Thanks guys!!