I had a 4000 lb camper on a 2005 F250 (had a 9800 GVWR) while towing 8000 lbs. Get an actual weight of your rear axle to see how much you have left with the current wheels. If you have the 10.5" Sterling rear axle, it is good for 9750 lbs if properly outfitted and is not anything to worry about. Since you do not have an upper overload spring, consider just replacing your spring pack with a heavier one. If it will need more help, then you can add StableLoads or air bags. You have close to 7000 lbs of tire rating on the rear axle - If you start to get close to that number, the rims and tires need to be upgraded and this is the time to look at 19.5" wheels. Since these wheels are heavier, OEM shocks will not have enough dampening, so you need to change to heavier Rancho or Blistien models at this time. I had the OEM stabilizer bar on the front and rear of my truck and never changed them out. Since you do not have one, look at the Roadmaster bars before the Hellwig.
