Ok so I just put on new tires, the old ones had 10.5 on them, the back tire was cupped so badly it was almost unrideable. Anyway I have since found out that cupping is generally caused by low pressure. Well before my 2700 mile trip I checked the air pressure and checked it once during the trip. Now after getting the tires back from the shop and installing them I checked the pressures on both and found that the shop had over pressurized (I think). Then I checked with another guage I have and found that one to be off/differant by 4 pounds. Pulled out another guage and it too was differant from the others. Ok so 3 pressure guages and (2 of them digital) all are differant. So how do I figure out which guage is good, and any recommendations on a known good guage. Thanks for reading this far.