I had something similar happen to me this morning at a stop sign going up a fairly steep hill. There were a lot of leaves underneath my tires, so I thought maybe there was a lack of traction. I don't know if I went forward and back, but I definitely had a hard time getting started. After I pressed harder on the accelerator (maybe 3/4 of the way down) the car proceeded normally. I've stopped at the same place maybe 50 times and never had it happen before.