When my wife was in town yesterday, I had her put mid-grade fuel in our SEL just to see if the higher octane might improve the acceleration from stop condition (shudder). She reported that she experienced the shudder for a time after she refueled. Today I took the car to a meeting and put about 30 miles on it, with several stop and go opportunities and I can report that it did not shudder once when pulling away in "D". I'm not excited about putting more expensive fuel in the car, but I will do so to get smooth performance. It make sense because the TCU is programed to up-shift ASAP to improve fuel economy and the shudder might be due to the engine actually lugging, as it would if you were driving a fully manual transmission car and you shifted from first to third at 15 mph. I'm still hopeful!