Putting a 12000# hitch on a Pinto does NOT increase its tow rating. As far as I know all TV manufacturers spec a max tongue weight for their VEHICLE. Note I said VEHICLE, not receiver spec. One hopes the receivers have a spec as high or higher than the VEHICLE spec. Changing the receiver does NOT change the vehicle spec, at least on any SUV's I've seen. As it happens I have the 2010 manual Ford publishes for their vehicles that can tow, it is part numbert RV-VER8535-0909. I'm sure they publish one every year. They are available at any Ford (or for that matter Chevy, or GMC) dealer. Sorry Passin Thru, but specs is specs and personally I do not ever recommend ignoring them.
As far as the 10% versus 13 to 15%, it is because of the hardsided TT frontal area. You are basically pulling a big sail down the road. If you are towing a boat, or popup, the frontal area is much smaller, and the 10% works.
Dry tongue weight really has no meaning once you load the TT, just as UVW isn't much help except as a starting point.
A 6000# TT needs a tongue weight of 780# to 900#, so you are ok there. As far as your GAWR, why not load up your Exp as IF you were going to tow, kids, dogs, gas, stuff, and all. Now find a handy scale, like at a bulk feed store or a sand and gravel supplier. Weigh your front and rear axle. Now assume you add 890# more to the rear axle weight. Are you within your Exp GAWR? If so, you are good to go. If not, you need a smaller TT or a bigger TV IMHO.
Hope that helps a little.
Chuck
Wonderful Wife
Australian Shepherd
2010 Ford Expedition TV
2010 Outback 230RS Toybox, 5390# UVW, 6800# Loaded
Not yet camped in Hawaii, 2 Canada Provinces, & 2 Territories
I can't be lost because I don't care where this lovely road is going