The wobbles are fixed on this one, I added some bolsters to one truck to take up the sideways rocking of the truck. It will still rock forward and backward, so it follows the track, but doesn't rock side to side. This arrangement fixes the body wobble, and still allows flexibility for less than perfect track...
The bolsters are just plastic scraps from a model kit that I glued to the truck in line with the mounting pin. The trick is to make them thick enough to take up the slack, but not so thick that the truck binds...
As is it will pull 6 scale/close to scale cars on level track no problem, and that will only improve with another motor, so maybe I won't need any additional weight...