If you have weird wear on your tires, I'd swap them front to back on each side. If the pull changes then you have your answer. If the tire is really strangely worn it should probably be changed anyway.

I was driving a friend's old blazer (with like 230,000 miles) and it was pulling bad (like to cramp your arm) and would shimmy like crazy at anything over 55. There was a weird bulge that ran all the way around the tire (near the whitewall) and I suggested he replace it because it looked perilous. Two new tires on the front and wow, the pull and the shimmy were gone. Really strange, I'd never seen that before and the pull I figured might be tires, but the shimmy, no way.

So swap the tires. It won't take you that long and then you'll have an answer.

But Sears still sucks.