I have a fifth wheel RV that I am pulling. The chart that I saw when I purchased the RV said that my total gross was 23500 (trailer and truck). My RV has a dry weight of 13??? lbs. It can handle upto 18000 which will put me over the total gross. 250 and 350 SRW weight limits are the same. Dually is more. I have also air bags on this truck. I am not worried about the trailer/bumper towing. I am worried about 5th wheel. I also bought a Contrex controller from Superchips to improve milage while towing. These are the only performance mods that I have made. I just want to make sure that I don't tear up anything while towing. Also the current 2011 f350 Dually comes with 3.73 ratio for towing. The 450 comes with the 4.10.