I bought my 2010 GMC last August and it came with some generic tires that the dealer installed new apparently. I noticed that one of the tires seemed to have a small leak, losing about 5 PSI per week, give or take. I figured it was the cheapo tires, and when winter rolled around and they became ice skates, I had had enough. So I replaced the no name tires with some Michelin LTX MS2 tires which seem to do a lot better in the snow. But now a week or two later, I am noticing that one of the tires is low again. I got the tires at Costco and they replaced the valve stems, so I don't think that is the source of the leak. I don't see any obvious dings in the rim near the bead. I'm baffled. Can a TPS sensor leak air?