Trailer brakes are a must. My dad has towed 10,000 lbs. in a 2,000lb trailer plus six men and all of our tools with his 2000 Ford F-250, which is the equivalent of a 3/4 ton truck. It had the power stroke diesel, and it would do 70 mph. Local hauling with a T bucket and a trailer like yours should be no problem with a 3/4 ton. As far as increasing the capacity, you'd have to change out the axle bearing and possibly the axle because of the bearing's capacity along with the suspension. You should be able to tell if you're going to overload the springs by loading the trailer slowly. Try your best to center the load, but if necessary, you could shift the weight a hair backwards to keep less tongue weight. The engine will handle anything. They used essentially the same drive line set up in the larger trucks too. It's not going to go anywhere quick though. I have a 70 GMC 1/2 ton that will in theory haul a 6000 pound bobcat with trailer. Although my truck does have the axillary leaf springs, it's still a 1/2 ton. You'll be fine with as long as you have the trailer brakes.
