Tire pressure should "ONLY" be checked when stone cold before driving - never after driving more thatn a mile or so unless you have a flat or other reason. They will naturally heat increasing inflation pressure as the vehicle is driven depending on load and operating conditions. The specified cold inflation pressure considers this. Proper inflation for your vehicle and tire combination should be on a decal on one of the door frames or the back of a door itself. They are sometimes located inside the glove box door. Most common place for CV's and GM's is the right rear door frame unless someone has removed it or the vehicle has been repaired after a collision. A good tire dealer will also have a complete reference for proper inflation of most vehicle/tire combinations if you cannot find the decal. As for your 37 psi, that reading is usless after driving 20 miles. Lastly, get yourself a good tire guage that stays in and gets regularly used on that vehicle.