Really need to post what year/engine tranny combo. I am not really knowledgeable about the ATs on the Regal but if they are anything like the ATs on the V6 models(LaCrosse/Impala), the electronics(TECM) are inside the tranny(right inside the cover/sump) and are being affected by heat. Transmission shops (at least the good ones) have specialized readers. You may want to see if you can get it to one and have them go thru the whole experience "connected" so they can evaluate. If it is the TECM, they are pricey and after installation may need to be programmed to the car before you even try to run it.