I don't know what kind you have, but i've used a few old ones, and they would just a sway left and right like a dogs tail fixin' to get a treat at anything much past 50MPH.
They seemed to settle down once you put some weight on 'em.. but I don't think the older ones are supposed to be pulled much faster than 55MPH anyway.
Not sure if that's the way the old ones are supposed to pull, or perhaps the few i've used have the same problem yours does.
>shrug<
