Howdy, my brother has an early 99 PSD with a 70 HP chip in it (sorry not sure who makes it) but anyway, if he hogs on the truck pretty hard (EX: towing up a steep incline) for any period of time the CEL comes on, after you let back out of it, the light goes off. Whats causing this? Oh, its an auto if that makes any difference. Thanks alot, Andrew