Under-the-hood CLUNK Transmission

I have a "Clunk" noise when my transmission downshifts. The tranny shifts smoothly, but when I reach around 50MPH or so, and the motor downshifts to normal RPM's (about 1500 or so), there is a Clunking noise that comes from under the hood, as well as an abrupt jerk. I believe that is a motor/tranny mount, or a CV joint. It clunks 8 out of 10 times. When I go to accelerate, it jerks on the upshift as if it were stuck or something, but again not all the time, but most. Fluid is okay and added Lucas oil transmission additive in it which is supposed to help with hard shifting, it did not. I really think is is something other than the transmission, due to it shifting so soomthly and being so responsive. Maybe even a modulator valve that is not allowing it to shift at the correct shift points??? Wish you guys lived around Cincinnati, and could help a feller figure this one out!! Motor does seem to jump a little while shifting through all gears while stationary. Also blatsted traction control light comes on and of while coming from a cold start, but once everything is warm stays on. All vaccum lines that run from the modulator to the SC are good with no leaks. This is very bothersome! Could the dummy light for the traction control have something to do with the clunk/jerk thing? Could the traction control be causing this, or visa versa? Thanks, Kevin

Topic moved to Series II Engine & Transmission Tech...

I used to get a jerking shift before I found a vacuum leak. Look again for cracked hoses, and replace. These are sometimes hard to find. Could also be failing transmission mounts, but that's more involved, so hope not. I doubt the TC light is related to the shifting issue.

I was also wondering if it could be a TCC soleniod?