The sticker in the glove box is likely assuming you have a 150 pound or heavier passenger in each of the truck's seat positions. Do you travel this way?
A majority of trucks hauling truck campers are over their GVWR, mine included. I am not over my axle or tire ratings, that's how most TC owners load their trucks, partly out of necessity as you are learning. My '05 Chevy dually has a GVWR of 11,400 but with my camper on and family in the cab I weigh in about 13,200. Hitching up the boat adds a couple more hundred pounds.
If you do want to upgrade the truck going newer will help, regardless of brand. Your truck's GVWR is 11,400 I think. Just 2 years newer, in 2011, it was upgraded to 13,000 pounds. Ford also had a significant increase in 2011.