1993 Saturn SL2 Electrical Issue?

Long story, but car starts and runs/drives great cold. Upon warming up intermittently trans either does not shift out of first, or is locked into 2 or 3, then slams down into 1st upon take off. I pulled engine codes "16 Info Flag-EVO Failure", "52 Info Flag-Battery Volts Out Of Range", trans code "65-Ignition Volts Out Of Range". With all lights on vehicle is overcharging 17+ volts at idle. Since trans works fine cold, and does not slip hot, I'm thinking the problem is the high voltage. Engine also stumbles on accel and sometimes revs up high during this shifting issue warm. I know these cars have battery cable problems, especially ground. I did remove an aftermarket set of duplicate cables from this car because cold their was no resistance to ground. What can cause the over charging (trans solenoid short, high resistance to ground on battery negative-car always cranks well and starts?) As I understand the voltage is regulated by the PCM? This car had electrical issues when I got it, so I ripped all the add-ons off and returned to factory wiring. I had this car sold, then buyer returned for refund because he thought it needed a trans. Do you think this is a trans issue causing the over charging or vise versa. I need this thing repaired ASAP, but will not put a trans in it. Please advise.