i know i know this is a mustang forum but here is my question. sister car is an 08 g6 gt, above 30mph the car seems to feel like it shudders/hesitates on acclerating. as she is accelerating it gets "jumpy" like its hesitating to go, you can feel it, hard to fully describe. dealership looked at it twice now and cant find anything, they did replace 1 spark plug. any ideas? or anyone have this issue?