Since you air tested the trans did you hear a nice thump when you applied air pressure to the front drum? Servo tested, ok? How about overdrive?
In my opinion there are still two possibilities one is a problem with overdrive direct clutches.
If the overdrive is good you will need to disassemble trans and check the front clutch. I have seen the front clutch not put together correctly and cause this problem.
Just my 2 cents.
