So, the air gage shows my tires at say 30 and the TPMS indicates 32 and sometimes 33. Which is more accurate? My tire gage is a pretty good one.

 

I have 3 different air gauges, and they can all read different, depending on total scale, accuracy, temperature, etc., but they all will be within a few pounds of each other..most of the time within 1 pound or right on. As for the TPMs, I would not trust them for absolute accuracy. I consistently have one that always reads a tad high, even though the tires are all checked and adjusted with the same gauge and at the same time.

I do stick with making air pressure adjustments with a single gauge, otherwise I would drive myself crazy.

I go further and inspect the tire wear pattern each year (or more often depending on maintence) with a vernier (tire tread depth) across the face of each tire. If I see that a tire is wearing more in the center, then I know I have the pressure too high. If more wear on both outer edges, then it has been too low. If wear on only one edge, time for an alignment...

Plasticman

 

Actually what I have read on Tire Rack leads me to believe that the TPMS sensors are very accurate, assuming they are in good working condition and have a stable battery.

 

the " exact " tire pressure could vary by + - 1 psi from one sensor to another, or one gage to another. Of course cheap gages are worthless.
The GM TPMS are very good. What they do show is the consistent reliability of relative pressure due to heat expansion. You don't want to be running your tires at 38 psi " HOT" . this can easily be checked at any time... Cold tire pressure means very little when you are trying to figure out why your tires are not performing or they are wearing out in the middle. Hot tire pressure tells you what pressure the tires see when they are actually in play. a cold tire sitting in your garage will never perform, or wear out, so why take cold tire pressure readings? the reason is its a relative reading. I set my tires to 26/27 in the summer cold so that when my tires heat up from the hot sun and roadway they will be where they should be, when they are performing.
The sticker on the door is for dummies. its there so that people wont put the max tire pressure found on the sidewall. At GM we called that the idiot proof sticker. Putting 30 PSi in your car will keep you out of trouble, but you can do much better with proper tire inflation, both for performance and for longevity. Perfect tire pressure will give you the optimum balance of designed performance, tire longevity, and better gas mileage. That's why tire pressure is monitored constantly and adjusted according to the track temperature at NASCAR, and all professional road courses where pit crews change tires.