I think you have found the culprit. I figured when I saw the pics someone had started a "hot rod" project and you are having to fix everything they lost interest in.
I see so many of these stall converter issues at the shows. Some dingaling in a chevelle has a small block with a radical cam and a stall converter that makes it almost undriveable in the car corral, so he spins the engine up, spins the rear tires and slings gravel all over someone else's car.
Partly cause it ain't easy to figure out which stall converter you need and mostly cause people think, "If a 2400 stall is good, a 3000 stall is better."
Sometimes trial and error is the best process, but that's expensive and tedious. Just as you thought, when you put the vehicle in drive on a flat roadway, you should have just the slightest amount of creep or forward momentum on a driver.
Do you know the specs on your engine? Post them here and I'll try to help or even better call TCI on the phone and they will tell you what stall you really need.
