I've owned diesel puck-ups since about 1990 and every year it's the same thing, about August the price starts to creep up because of the stockpiling of home heating oil. If it gets really cold somewhere in the U. S. then the price goes up pretty quickly for a while. The good news, at least for me, I take most of my vacations in the spring and early summer when the price is at it's lowest.
Dave