I'm thinking a fuel supply problem from the rear tank....
Reasoning:
Engine not getting enough fuel, you are pushing harder on the throttle. The FIPL sees this as a hard acceleration (even though you aren't gaining speed) the TECA keeps the torque converter unlocked, which generates heat.....
You switch to the front tank, the engine is getting enough fuel for demand, you ease up on thr throttle to maintain speed, the TECA sees the FIPL at a lower level (not what it thinks is a hard acceleration) and allows the torque converter to lock. This in turn lowers RPM and heat being produced in the transmission.......