Using your OBD-II software, are you able to monitor the Vehile Speed Sensor (VSS)? This might be your problem, just a thought.
One other thing that comes to mind, as a possible cause is the Turbine Speed Sensor, located on the pump. I have read of simialar problems being resolved by replacing that.
As for the EPC solenoid being cut off after a fault is logged, that is just the PCM going into Failsafe Mode for the transaxle functions. IIRC, and I probably don't, the line pressure is held at 90 PSI when operating in failsafe. Hince the reason you can squell your tires, during those times.
Anyway, welcome aboard and keep us updated on your progress.
