Check all the ground on the motor and the battery, also check the tranny too. Make sure the battery clamps are good too. Make sure the battery is grounded well too. Pull your knee pannel on the drivers side and make sure the grounds are good there. I would get a helms and find all the grounds spots in the car and make sure they are clean and not corraded. Did you check the factory alternator? Make sure its putting out 14.4 volts at idel and no more then 15 with the tb open up half way.