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I have just purchased a 2013 Grand Sport coupe. It pulls to both the left and the right....sometimes hard and sometimes almost un-noticeable. I had it aligned at the local chevy dealer and it improved somewhat, but I am still fighting the wheel. It seems worse on country roads than smooth interstates.
Agree on the tires. The GY's on my C5 did the exact same thing - changed the tires out to Hankooks and the problem went away entirely, and they are QUIET.
On my '13 427 'vert (essentially a Grand Sport with the factory ZR1-sized Mich run-flats) I get some very subtle tramlining occasionally especially on roads with a center crown in the lane. The size of the tire (especially the width), profile, wear, age, type of tire (run-flat vs non-run-flat) and temperature all have an impact.
Lots of information here on alternatives depending on what you want to accomplish. The Goodyears don't have much of a following here. Chevrolet changed to the Michs for a reason, and there are many good alternatives out there beyond that. Tire Rack has a lot of good info for comparison.