Well, I went to get in the car this morning, and the pass side rear tire was nearly flat. I took the tire off the car and checked all the way around and there is no apparent damage or puncture. Since I couldn't find anything, I just aired it back up and went to town. After about 5 hours of sitting I decided to check the pressure again, and it's down almost 15psi already. Needless to say, I'm slightly concerned since this comes soon after taking the car well above 100mph a few times. I'll take it to a tire store tomorrow to have it checked out, and hopefully they can find a puncture or some other good reason why the tire is losing air, and not just tire failure.