Help: 700r4 Troubles

[West Texas Z]

Asking this for a friend. Its a 79 Chevy Shortbed.

Ok, dropped my TH350 and replaced it with a 700r4. Swap went fine, but I am having shifting issues, TV cable has been adjusted and re adjusted, I am pretty certain it is where it needs to be. TCI lockout converter installed.

I have reverse, and first all the time, I have 2nd and 3rd for a stop light or two, then they go away, rarely have the OD 4th gear. I can readjust the TV cable and get 1,2,3, and 4, but 2,3,4 go away after a mile or so. readjust, then they come back for a mile or two, then go away again....
also, shifts are nice, not soft and stacked, they are spread about where they should be.

Hope this is enough info to get some feedback.

Pulling my hair out over this...

ANY ideas???