I'll second what DmaxMaverick said with one exception - your tire man might actually be an 'imbicile' rather than an 'idiot'.
Most tire mfg's websites have tire load inflation tables that you can download for the reasons he stated.
2003 K3500 Crew Cab, Banks Stinger Pkg, Exhaust Brake & Exhaust, OilGuard Bypass filter, Lube Specialist Secondary Fuel Filter, Allison Deep Pan, TTT Mirrors, B&W Turnover Ball and Companion Hitch, Truck Trunk Sliding Box and V-Box, LINE-X, Co-Pilot Live GPS, Hitchhiker 31.5 LKTG 5th Wheel 28' Wells-Cargo Gooseneck Car Hauler