need some trans help..tf3 won't upshift

Fishy gives good advice & insight here. I'd venture to say he's probably done a few more of these over the years than I have. If I could just throw my 2c in. FWIW I had a 727 that gave me very similar problems after a VB & servo modification & it turned out to be leaking servo. I fixed that & it worked fine afterwards. Air pressure test is what found it. Good luck. HTH.