You are asking all the right questions and the answers are not so intuitive.
Remember firstly and lastly, for a given set of conditions, and total drag, the dmax is going to find the power to exactly offset the drag for steady state conditions. If you lower pressure, and do nothing else, then the truck will have to have more pulse. Or you will have to command more pressure with pedal. Keep digging into these concepts. It is a great (albeit painful) learning curve.
Thanks, I'm never finished, only finished for a few days at a time haha.
Peace Through Torque
Punisher Performance DSP5 Tuning, PPE Dual CP3's, 68mm Fleece Cheetah, Punisher Built trans w/ Suncoast Parts, Airdog 165, SoCal 100% Overs, ARP Studs