The TH350 in my 70 El Camino has about 10,000 miles on it since a rebuild and has worked fine until yesterday. The trans will not downshift into first gear when coming to a stop. It will shift if done manually. Fluid level is correct and the modulator is plugged in. Since it started acting up the shift points under part throttle are slightly higher, but that's all I've noticed.

Any clues? Thanks.

Sounds like sticking governor or shift valve troubles. It may require disassembly of the shift valves and a good inspection and cleaning of them to make sure there are not any burrs on them if the governor is okay.

Thanks for the reply Steve. Can you clue me in as what to look for? I was going to put a governor spring kit in it anyway to raise the shift points. As far as the valves are concerned, are you talking about the valves that slide in and out in the valve body? Could it just need a oil and filter change? Thanks.

The shift valves are in the rear of the valve body. Often it only takes a tiny bit of debris or a very small burr on a valve to hang it up. You will need to pull the valve body off to check them though. They are held in by pins that come down from the top. Be very careful if you take them out so as to keep them in order. Do not round off any edges on the valves, they need to be sharp and square, just look for debris that can be cleaned out. My advise is to get ahold of a good manual to see what goes where if you do this yourself, or look here (http://www.tciauto.com/instructions/326200_inst.htm) for a look at where the valves are at. It shows the 2-3 valve location, the 1-2 is next to it, towards the center of the valve body. Starting from the drivers side of the valve body the valves are 1. pressure regulator, 2. 2-3, 3. 1-2, 4. manual low, 5. detent.