[J-Ri]

Vibration probably is out of balance/out of round tire, possibly bent rim. Check all. The tire wear sounds more like just low inflation than camber, especially if it's both inner and outter shoulders that are worn. Camber would have to be off by a lot to affect wear. 5 degrees would pull very hard, and imagine 5 degrees across the width of the tire, probably only 1 or 2 32nds side to side. Walmart tires (everything, actually) are lower quality, they tell the manufacturers what they'll pay for something and if the manufacturer can cut corners enough, Walmart sells their stuff. Rotation depends on tire type. Radials should only go front to back... sortta. They need to rotate in the same direction all the time, so if you want to criss-cross you need to flip them around on the rim. Something about the direction of rotation weakens the steel belts and they can blow out if reversed. I don't know about that, just what I've heard. I only run directional tires anyway...

As for tire pressure, the reccomended PSI in the door opening is for the best ride. You'll get better handling, even tire wear, and better gas mileage with higher PSI. I keep mine at the maximum labeled on the sidewall. On my Cavalier's 205/55/16 that's 44 PSI and they wear perfectly square, and that's with considerably more camber than recommended