excessive trailer-hunting at 55mph

Hi Fellows,

i often pull a trailer on my M535i to carry my mudracer to and
from the track,
unfortunately i have severe trailer hunting problems at 55mph. No matter how i
changed the position of the cargo on the trailer on my last run to Western
Kentucky it never did run as smooth than behind my fathers
yellow Siverado.
Other people say that such kind of compact car isn´t suitable to pull a
under loaded 4000lbs trailer. How about your experience of pulling with an e28?

Kind Regards,

Ken