Picked up a new T120. Run great till I took it in for the 500 mile checkup. The bike now surges. Real pain in lower gears. Going around corners in 1st or 2nd gear the bike bucks. Could dump the bike if gravel or wet. Can not hold a steady speed without surging. Took it back to dealer and they said it run fine. They stated all they do is change oil and do a readout which passed. Is it true that is all they do? Thanks