Increasing Payload by swapping out my Truck Bed

From what I've been able to find out, best estimate using numbers from fleet.ford.com for an entire bed is 475 lbs. http://www.ford-trucks.com/forums/869554-how-much-does-the-bed-weigh-frame-rust.html

I think you probably can't save over half that at most or 238 lbs. I doubt that's going to be worth it. I think it would make more sense to upgrade the tires/wheels if you are worried about weight capacity.