The other item the tow rating will not take into account is the cargo carrying capacity of the truck. The DRW will have significantly more cargo capacity than the SRW truck due to heavier springs and axle. On 2013 trucks this is almost a 2000 lb difference between a SRW truck and a DRW truck. If you are going to buy an F250 truck you will hit the cargo carrying capacity of the truck before you hit the maximum towing capacity. You need to determine what your fifth wheel pin weight is and how much additional cargo you are adding to your truck and compare this to the cargo carrying capacity of the truck you want to buy ... you also need to know what GVW the truck was built to (on the door sticker of the truck) ... F-350s come in multiple GVW classifications depending on how built and how ordered.
