Towing limits ?

[bard@domain.elided]

What are the towing limits for my '77 Scout II with a class IV hitch and
a set of add-a-leafs all around ? I was wondering because I often tow
about 7500# of airstream
around. The trailer has equilizer bars, electric brakes {new}, and a
sway bar and generally pulls like melted butter. I only have problems on
intense grades or in Wyoming {Gale force} winds. What suggestions does
anybody have for improving the handling class in this case ?