Find yourself a 1993-1/2 or later grand cherokee with the straight 6. It had the first RE trans in it. The V8 GC had the RH trans. These RE's had a standalone control module to run the trans. It took inputs from the engine controller for TPS, temp, etc. The TCM "makes" the gov psi by using a PWM solenoid and reads the gov psi by using a pressure transducer. These early units had a thermistor on the harness in the pan, later we went to a pressure transducer having a built in thermistor. The shift schedule is mapped. 1-2, and 2-3 are all controlled by this map using gov psi and it's fight against throttle pressure. You don't control shift quality using gov psi or throttle pressure. You get hard shifts because of high clutch capacity versus anticipated engine torque. That's why sticking the throttle lever back and then driving around town gives you harsh shifts, low torque going in to the trans in anticipation of high power levels coming in and not being realized. The 3-4 shift is all done with electonics - we spike gov pressure to force all the 3-4 valves over then hit the OD solenoid then the LU solenoid. There are lots more controls than this - this is a summary.