It seems that no matter what trailor I seem to haul, once I get up to highway speed, the trailor starts to wag. Large or small, they all wag, back and forth. I see it on the road alot, some construction trailor loaded with some mid-sized piece of eqpt., wagging back and forth down the road. What is it? Is it the placement of the load, or the lenght of the trailor, or what? HELP?