Hello David,
By any chance does your rear diff have a track-loc in it??? Does it do it
worse when hot??? If so it is likely the LS clutches chattering. There are
additives to prevent this. I solved a similar problem in my Scout with the
Mobil 1 gear oil. I espically noticed the problem when pulling a trailer up
a grade with a lot of switch backs or when pulling a trailer onto the road
from the sholder (similar to you pulling out from a mail box).
For your use an open diff would probably be best as I'm sure the dragging
clutches don't help your gas milage or the wear and tear on parts.
Tom Reed