transmission troubleshooting

[bdriven]

Hello guys,
so last week, I finished rebuilding my transmission (4.4i, 2000), 5hp24.
my original failure was that reverse was slipping. not engaging at all.
I bought a banner kit, replaced all clutch discs and seals. I did find the snap ring loose on the reverse clutch pack. I also rebuilt the valve body, replaced o-rings, gasket, the ball bearing, the tiny discs and such.
so, at first, I was happy, reverse worked, for a little while, then the same problem, reverse sometimes slips, sometimes it doesn't.
when going forward sometimes slips a bit from 1st to 2nd, and one can sense a delay when accelerating.
What could have gone wrong?? did I miss something???
Thanks!