That's cause the tire shop owner is in the business of selling more tires. Did he put them on too narrow of rims too, to help accelerate the center tread wear even more than the over inflation would?
Realistically, say 35psi holds up the front of the truck just fine now on OE size pavement pounder tires and what, maybe 30 in the rear? (I'm running 42F/37R right now on 255s P tires on my new half ton, for a bit "stiffer" ride.)
Enlarge the tire and the carrying capacity per psi goes up with the increase in treadwidth and sidewall height.
Quick guess, with 35s you could easily run 30F/25R for a comfortable ride. Air up from that a bit if it feels too soft.
