Is lifting 280 lbs off of a 4,780 lb front axle significant to handling?
No! However what is more important is how much weight was on the axle before and after the tongue weight was/is added. 280 pounds taken off the diesel engine heavy front axle probably will help with handling. And since the truck came with a significant front to rear axle bias adding more to the rear and taking a little off the front will likely work better. Been there done that. Even though some hitches incorporate both into the hitch, sway mitigation/control is not weight distribution and you might still want to check into a sway system.
As to the receiver it should say somewhere on it what it is rated for both max tongue dead weight and max weight using a WD hitch system. I suspect the 1500 pounds is with a WD hitch. If you want to go to the incredibly safe side Tork Lift makes an aftermarket receiver rated up to 30,000 pounds towing and 3000 tongue weight.
Load the trailer so that you have approximately 15 percent of the total weight on the tongue. That tows very well and helps combat sway. Too little tongue weight can aggravate a sway situation.
With the trailer, you still have plenty of rear axle capacity so don't be afraid to add a little more tongue weight. And the Cummins is a towing beast so you will never run out of power towing your trailer.
