I found that mine did this due to the rear-most exhaust hanger rod being too long. I cut 1.5-2 inches off and then welded the ball tip back onto the end. They stay centered now. Before going through with it, I wrapped a bit of duct tape around the hanger rod to build it up. I worked my way outward until the hanger would stay centered after a few miles of driving. That way I knew how much to cut off.
2012 Kona Blue 3.7L V6:
Borla LT headers, O/R h-pipe, Borla S-types, 3.73 gears,
Steeda adjustable UCA w/ mount, BMR LCAs, Airaid CAI,
LCA Relocation brackets, AE driveshaft, GT 80mm TB,
Black 18x9/10 2010 GT500 Wheels w/ Nitto NT555s,
Eibach Sportline Springs/shocks & Koni STR.T Struts