Slipping 2-3 shift

You say you have a 904 trans & fitted the TF-2 Shift kit from TransGo right? If I can remember correctly the TransGo supplied orifice is only fitted to the 727 & not the 904. If you fitted it, this might be causing 3rd gear delay & engine flare up on the 2-3 shift at part throttle.
Cheers. Gaz