Do a line pressure test. Pull the plug on drivers side of trans its just above the pan foward of the control of trans. Install a press gauge.
Spec.
Line Pressure Idle
p,n=50-65psi
r=70-100psi
d,2=50-65psi
1=70-100psi
Test with trans up to temp.
Total pressure tests 6.
Post your findings for further testing to pinpoint your problem.
BILL