I am having engine ping problems. There are no PMC codes and I have checked the fuel press with koer and koeo, pressures are within normal range.The water temp is on the low side of normal. It is occuring when I'm pulling my fifth wheel trailer. It pings on the Straight and level over about 60mph and when going uphill. If the a/c is on it is worse and it looses power down to about 45mph. The outside temp is about 75-85F.
The Truck was ordered from ford with a towing package and itis equipt with a eng oil cooler and trans cooler. (the trailer weight is about 7500lbs fully loaded)

I apprecriate any help
Thanks
Shady