The monthly OnStar Vehicle Diagnostics Report that I receive via email includes (as well as other diagnostics) tire pressure on each of the four wheels that seems inconsistent with readings I have personally measured on each tire. The email I received today indicates three of the four tires are reported as having 33 psi and one 32 psi. I checked the "cold" tire pressures today with two tire pressure gages and both indicated all four tires are at 35 psi which agrees with what I set them at (using one of the two gages) a couple of weeks ago. I have seen the same trend before where the Onstar report has been lower than I have measured. My tires are the standard factory installed 18" Michelin Latitude Tour kind. Has anyone else experienced a similar difference or have an explanation for the difference?