I run airbags on my truck, not because I over load it but to level the truck back out when it is loaded. I have a small 3" lift installed in my truck and it sits level with nothing in the bed, but even with a 550lb ATV in the bed it squats noticeably (about 1.25"). With the 900 lb TW of the camper (with Reese dual), and a couple hundred lbs of firewood and misc in the bed it is very noticeable with the rear down about 3.5". But if the truck had the stock rake (front end down, rear end up) the rear would only be 1/2" low.
Mine has 5000lb Firestone Ride-Rite bags with a Airlift Quick Shot air system. With 35 lbs of air in the bags (and WD hitch on) the truck is back to level.
TT-2013 Passport 3220BH
TV-2004 F150 FX4, not exactly stock...
with 2001 Kodiak K215: 2010-10, 2011-12
with 2012 Grey Wolf 26BH: 2012-19, 2013-24, 2014-11, 2015-6
with 2013 Passport: 2015-13, 2016-15 booked