If you're talking real world payload and not stickered payload which has class limitations in a 3/4ton, then the diesel doesn't really subtract much of any as it's pretty well centered over the front axle.
But the newer 250s have a comparatively soft rear spring rate in my experience. My 2013 with an estimated 12-1400 lbs in the bed and about 500lbs of tongue weight would squat pretty good. They hold well once on the lower overload leaf but are riding really nose high by then.
All easily rectified with some help for the springs. Rest of the truck will handle more.