Anyone ever have this? in slow moving traffic maybe 10-15 mph when the engine rpm is 2k and car is moving slow and I gently accelerate (because its bumper to bumper traffic) the back of the car or trans seems to shudder or shake? I had replaced all 8 the spark plug coils earler this year. But its only in stop and go traffic or if I slow the car to almost a stop and accelerate slowly.. Any ideas? I love the car it rocks and have had few if any problems..