The circuit at the transmission controller that the OP is trying to power only controls the governor pressure sensor and the transmission fluid temperature sensor. These would be very low current draw circuits. The various solenoids that control pressure in the transmission are controlled by the transmission relay in the PDC and its separate circuit to the transmission. Review diagram page 8W-31-2. I am puzzled about the mismatch in wire colors from the 1998 Durango wiring diagram and your vehicle, a 1996 Dakota. Is it possible that the engine and/or wiring harness has been switched from another Dodge vehicle (different model year) and the connectors are the same but the wire colors are different? The only other 5 volt reference source at the PCM is connector #1, cavity 17. This powers the cam position sensor, crankshaft position senosr, throttle position sensor and MAP sensor. You could rig a wire from this cavity and power cavity #31, PCM connector #2 and see if the problem disappears. Would that be excessive load on the PCM connector #1, cavity 17 circuit considering the number of sensors? Have you checked all of the male and female terminals and connectors that are involved? Dirt, corrosion could be causing voltage drops and maybe that is what is causing the transmission controller to enter limp mode?