My passenger rear Mich PS2 got slashed by debris on the highway recently and was replaced at 13k miles. I later learned I should have replaced both rears with that much difference in mileage/tread (car def feels a tiny bit "squirley" on the highway now). So I plan on changing out the other rear and when I checked the tread it has 3/32nd" on the innermost tread, 4.5/32nd" center and 5.5/32nd" outside. Is that enough of a variance to suggest an alignment issue or is that fairly normal for a 997 C2S? The fronts are all wearing evenly. Thanks in advance for any advice.