Hfactor:
The first question is "is it really a 5000lb boat? Have you had it weighed?

My boat dealer claimed the manufactures web site was wrong, and the boat and trailer couldn't be over 6000 lbs and he didn't know why the trailer was pushing the back end of my Excursion to the ground. I did! When I got the boat & trailer weighed, my 4900lb boat tipped the scales at 7250lbs with 1/2 a tank of gas (100 gal capacity) and had a tongue wt of 840lbs or close to 12%. He didn't want to believe the #'s. I towed with a w/d hitch on the boat trailer and didn't like it at all. The surge brakes didn't work the way they should and I still had tooooo much tongue wt. After several attempts to "work out" the problem with the dealer, I finally bought an alluminum triple axle trailer with electric over hydraulic brakes. This cut my weight by 1000lbs and reduced my tongue wt to 400 lbs and gave me a set of brakes that I was sure could/would stop my trailer from coming through the back window.

The moral of the story is, yes I could tow the 7250 - 8000 lbs fully loaded trailer with my Excursion, but was I comfortable? The answer to that is not always. If I was trailering to the FL Keys to relax and getting there was making me tense, I was defeating the purpose. With my new trailer that balances the boat and eliminates the jerking and surging of a typical large boat trailer, I can go anywhere. I now have a 30-35% reserve on what Ford says that I can tow. I can tow in O/D and maintain 65-70MPH (2000rpm) and still get 11MPG . With the extra wt, I couldn't stay in O/D and when the road got too hilly this required locking out O/D dropping my speed to 60-65 (3000rpm) and then getting 7.5MPG .