Yet another problem. Well, the car sat in a field for over a year, so some problems are to be expected.
This one is like this: The TCC (torque convertor clutch) locks up at about 45mph, which is about right. But when it does, the car commences to jerk and chug. You can tell it'* the TCC because a light touch on the brakes disengages it, RPMs jump by about 200 to 300, and as long as you keep your foot lightly on the brake, everything smooths out. Otherwise it'* like the TCC is engaging and disengaging very quickly. Transmission guys--is a new TCC solenoid called for? And how hard are they to replace? I probably need to replace the trans filter anyway. Anybody have pictures of the trans with the filter out and the TCC visible? It'* about time for a Dexron shampoo

Put some seafoam trans-tune in there and run it for about 500 miles. After that, drop the pan and change the filter. This will end up replacing about 1/3 of your fluid. If this doesn't solve your problem, I suggest a professional flush (80-100 bucks). If all these fail, you're looking at a rebuild.

Don't use synthetic trans fluid. Seriously consider adding an aftermarket trans cooler.

So with your foot lightly on the brake, you can go above 45?

With the brake on that lightly its not going to slow the car just trick the trans from going into overdrive or torque lockup

There'* a pressure switch like the taillight switch that touches your brake pedal arm. When you push even lightly on the brakes it is supposed to (and does in this case) release the TCC if it'* locked. In fact, if I wanted to I could just adjust it so it'* out far enough that the TCC never locks, but that would adversely affect gas mileage and transmission wear. On the other hand, this is mostly an around town car, so maybe that'* what'll happen if the suggestions above (Sea Foam and flush) don't work. I don't particularly want to rebuild the trans on a $500 car....
Thanks for the advice.
Keith

Glorcar--you have a Mustang with a small block Chevy in it?! Cool 'cause it'* unusual.

Well, thanks to the knowledge base on this board I was able to fix this problem. It wasn't the TCC at all. I did a search and found many other people had this problem and it was usually ignition related. That makes sense, because the TCC locking up puts extra strain on the engine by eliminating torque multiplication through the torque converter--it'* like lugging it down when you have a stick shift. If you're not getting good spark the engine will buck and stumble. I read that and said aha! So I got three new ignition coil packs, installed them, and the problem disappeared. Plus the car accelerates better and gets better gas mileage. So, thank you. I'm glad I found this board.

Very cool glad you got it fixed! I have a similar situation with my 2000, but I'm gonna try trans Seafoam first. However if that doesn't work I'll take your discovery into consideration.