I rebuilt my transmission 6 years ago and added a TSX 6th gear to my 5spd EP3 tranny. I replaced a blown 2nd gear and any synchros that needed it.
Upon assembly, from the first time I drove it post rebuild, 5th gear would not stay in unless I was completely off the gas. As soon as I touch the gas it slips out.

It does not grind, just slips out. I have dealt with it for 6 years but now that the tranny is out, I want to fix it.

Does any one have any ideas?

I considered that I forgot to replace the ball and spring for the shift fork, but they are all there.