Replace '91 auto trans with a '94 trans?

What would be involved in replacing the 4 speed auto trans in a '91
Caravan, with the auto trans from a '94?
Both vans are 3.3L, FWD.
My research indicates there is some difference between these two
trannies. Would changing the TCU solve the problem, or are the
wiring harnesses different?

Chrysler torque converter/transmissions have SO many problems even when the correct parts are used, are you sure you EVEN want to think about introducing another opportunity for failure?