I was doing an OT event at CMP this past weekend in my mach1 street car and running Falken 615s in 275/40-17. The tires were getting pretty thin when I arrived and Sun at lunch I rotated front to back because the tread sipes had all but disappeared in the middle on the rear. When I went back out on track the car felt unstable and grip was really reduced.Also when I pulled the shifter from 2nd gear the car would move to the right a little and I hadn't even gotten it into 3rd yet. This was happening in a straight line while accelerating hard after coming on to a straight. I began thinking something had broken or worn out in my rear suspension or rear end but now I'm just thinking it was the tires. Any thoughts out there? Also I can tug and push on the rear wheels and it feels like there is a little bit of in/out play and it is the same on both sides. Is a little bit of play normal?