Is it bunny hopping, or just running jerky? If it is hopping check the quartering of the drivers. In other words, make sense the 'weights' on the three drivers on each side are at the same relative position. If they are not, the running gear binds, and the loco just about leaps off the track. You can move them a bit on the axle with your finger. If the hopping goes away, put the tiniest grop of CA on the en of the axle of any wheels you moved.I haven't had a chance to break it in yet, but for the ten minutes I had it going back and forth on two sections of flex track, it's jurky at low power, and has a spot that I need to give it a push if starting. Hope an hour or two around a circle track with loosen it up a bit