still trouble with 2-3 shift

Well there are no check balls between the valvebody and the case.
Several things come to mind though. It could be in the valve body, possibly this is an older DC conversion valvebody that needs the accumulator bore vented at the top, you have somewhere that the fluid is leaking by and applying something it's not supposed to or the band is not releasing properly.

I would put a different valvebody in first to see if that cures the problem, if not I'd probably pull the trans and take it apart for inspection.