T-727 Problem

Just replaced T/Conv with a 3000 stall unit.Now after 30 miles of driving it will not engage in any gear. Come out next morning and let it run in neutral for 30 sec and it works great.All fluids are correct. Starts in Park and neutral then. No leaks at all. Is the T/C bleeding down,or pump begining to fail ?

Then come out next morning and it will not work in any gear....come back in 6 hrs and works fine after running in neutral for 30 sec.

I really do not want to pull this apart again,especially after spending $$$ on new 727 and TC

Car is a 1970 340 Duster