Some tandem axle trailers will weight transfer between the axles rather
than putting load on the tongue when the tow vehicle is lower than
normal. ie when you go over a hill it will unload the hitch at the top.
Makes for a very exciting down hill run.

Unhook the trailer, let the hitch sag down to the ground. It should have
the same hitch weight as it started with. If it just hangs in the air,
you have trouble. Only way to fix is to make sure you always have at
least some load on the front, say with a big tool box that is always on
the front.

Steve Hopper wrote:
For anyone out there who knows about trailers:
Last year I bought what seemed to be a heavy-built,
double-axle trailer. While towing it home with
my Full size Chevrolet long-wheel base truck using
a 2" receiver, the trailer pushed the truck around
whenever I got above 40 mph. It seemed to 'fish-tail'.
I had no load on it whatsoever, but the tongue load
seemed higher than my other dual-axle trailer.
Would a too-heavy tongue load cause this fishtailing?
Many thanks. sdh.