Test cooler flow with the trans in gear, ( block wheels, have someone in the car on the brakes ) some trans don't have flow in park, not sure about the 722.6

A bad TC will just give poor acceleration ( slipping stator sprag ) or drag the motor down at higher speeds ( locket stator sprag ) .

What were the specific slippage codes?

You need to put a line pressure gauge on the trans and look at pressure prior / during the fault.