You're right, I didn't account for any weight of passengers, which again adds to my problem. Like others have said, I also agree that the curb weight of the truck is low based on the options i would most likely put into it.
Sorry to drag this discussion about the axle rating out, but just so I understand, a Ford Sterling axle found under an F-350 SRW has a 9,750 lbs rating, meaning I would not expect overload related failure up to that number. Ford only rates it up to 7,250 for whatever reason they choose?
It seems like a few guys out there have more than the 7,250 on their F-350 SRW axles and with appropriate suspension and tire/wheel upgrades seems to be handling it okay.