Curious thing happened on the way to work....off the hwy after traveling about 15 miles and accelerated thru a gradual turn in 4th gr(2006 C4S) when the car started to buck and run rough.....tach stayed steady and then came to a stoplt. Steady idle and accel fine thru 1,2 3rd gear even giving a little more throttle than usual. Hmmm...fuel pump issue? vacuum leak? bad gas?? Any ideas?