2012 Expedition EL w/HD tow package, longest travel trailer?

I have a 2007 Lincoln Navigator L with the HD tow package. I would suggest you weigh your vehicle and trailer. I have taken many weights on our TV and loaded trailer and am under all of the weight limits(barely) except for the rear axle, for which I am 100+ lbs over. I am right at the limit on the hitch weight. I am in the process of upgrading my TV to an F250 or F350. I love my Navi and hate to get rid of it but I feel that for the safety of my family I must do this.