Background-two separate symptoms: 1) My Denali has about 32K miles on it and IMO it has always had a slow response followed by jerking acceleration. When I took the car into the dealership for an unrelated issue, the service manager, who was riding with me to diagnose the unrelated issue, told me that the jerking was because the car was getting used to how I drive and once it knows my driving style the jerking will stop. He was right to a certain extent. However, the car still is slow to respond, especially when starting from a stop. 2) About a week ago I noticed an intermittent vibrating periodically on the right side of the vehicle. A lot like when driving over those "wake up" strips before coming to a stop sign or when you drift too far off the road. There was also slight vibration in the steering wheel. I didn't think too much of it until I took a drive along a long, relatively even, road. During the drive, the vibrating became cyclic, occurring after one full rotation of the tires (or close to it) for about 20 miles. I then hit a very strong thunderstorm for about 25 miles and when I got to my destination the symptoms stopped completely and didn't start again for 36 hours. Now the symptoms are intermittent with no associated patterns that I can identify. I would like experienced opinions before taking it to the dealership...is my transmission slipping? thanks in advance, Kim.