C4 rev manual valve body 2-3 shift problem

Over the last few months I modified my tranny into a reverse manual valvebody from ArtCarr
Last weekend I got to drive the mustang with the modified tranny.
It all seemed to work fine, but then when I went from 2nd to 3th gear I feld the tranny disengaging the 2nd gear. The engine rpm went up(so I immediately backed off on the throttle). But it took almost 2 second to go to 3th gear (it sits in some kind of neutral), causing the increase in engine RPM.
A very long 2-3 flareup (2 second)

I drove the car shifting though the gears for about 30 minutes, but the problem remains.

For the rest the car behaves perfect, but the problem must be dealt with.

I am already in the books, trying to figure out the problem.

Anyone there with a good advice?


Harry