Bman

I have a stock 1997 Trans Am with about 125k miles, so it's well broken in and I don't think the engine and trans have ever been rebuilt. I was getting the P1870 code and replaced the valve body with one that had a SONNAX TCC valve, and that's made a nice difference in regular driving. If I go full throttle though, it starts to run out of breath approaching 5k rpm and holds the gear longer than I think it should. When it finally shifts it puts you back in your seat again, but will hold 2nd longer than I would like also. Is this due to something else in the trans being worn, or is there something that can be adjusted?