Trans problem, need advice

The tip off tho is no reverse.

In reverse all pressure regulation is bypassed so whatener the pump puts out is what you get, usually over 275psi.
In reverse the hi-drum is engaged and the L/R band, and nothing else.
In manual low; the Forward clutch is engaged and..... you guessed it the L/R band.
So the only thing those two have in common is the L/R band. Tighten her up and see what happens.