If you run too high a pressure the truck will handle badly, I would run around 50 in the rears unless I had a big load on. Lower pressures improve grip, handling, wear when unloaded. As far as the warning lights go, if changing the sensors doesn't fix it I would put tape over the light and ignore them. I would service the parking brake to make sure it works properly.
Brian
2005 F250 Supercab, Powerstroke, 5 speed automatic, 3.73 gears.
20 ft race car hauler, Lola T440 Formula Ford, NTM MK4 Sports Racer
1980 MCI MC-5C highway coach conversion
2004 Travelhawk 8' Truck Camper