I did some testing today with the tuner and without. The conclusion I've come to is these engines defuel at 1500'F EGT. I tried with the tuner and egts got to 1550 then backed down to 1500 and stayed there or just below. Also a noticeable drop in acceleration when egts were staying right at 1500. Without the tuner it was the same story egts crept just over 1500 then backed down to 1500 or just below. IMHO a tuner is going to give you no added power towing up a long grade until other changes are made. Also noticed the tuner increased my egts only 50' climbing the same hill at the same speed. I'm thinking the high egts are the reason for the high coolant temps some are seeing pulling up hill also the defueling would explain losing speed at the top of a grade some people have talked about. This is just an observation I had. It was consistent every time I tried it. I think more air or some deletes are in order to get the most out of this engine.