Torque Converter Lock question

97 Caravan 3.0l, 3 speed. Code p0740 came on (no lock-up). 2 days later,
transmission would not go into gear at all. Transmission shop replaced
transmission, said gears broke. New tranny shifts, but will not lock-up.
Code p0740 on again. Seems odd to get same code on new tranny. I suppose
the tranny shop could have transferred a bad solenoid from the old tranny to
the new (which they deny). Is there anyway for a weekend mechanic to test
if the tranny lock-up connector (by dipstick) is getting correct signal from
PCM? The difficulty I have is determining if the fault is with the
PCM/wiring/connection to the tranny, or in the tranny itself. Can a dealer
test for proper operation with a DRB? Or re & re another tranny ?$?$?$
Thks.