JIMLIN - You're assuming that all the payload weight will be on the rear axle. In my opinion that would be nearly impossible to do. First you'd have to leave the wife and kids home (or make them ride in the bed of the truck behind the axle) and absolutely 100% of the payload would have to be behind the rear axle. Even if you could somehow manage to load 3240 lbs behind the rear axle, as far as a TT is concerned, a simple WDH would take care of the extra 323 lbs. by transferring weight to the front axle.
All in all, not a very likely scenario.
The biggest joke would be trying to load 100% of the payload on the rear axle and none on the front axle.