Moved to proper section.
A trans cooler wont help if the PCS is going bad. Have you had the car scanned? Some trans codes don't trip a SES light. I've fixed many hard shifts by removing the shift accumulator and scuffing up the cylinder walls a bit. Go to the tech info section and look for transmission. Then look for installing a shift kit on a 4t65e transmission. It will explain how to do this.