You have less than the specified 475lbs of rear-axel load the truck was designed for (you are at 460lbs , if I added right), and there is a safety margin of ata least 10% (unless the weight of the gas throws something off?). I'd guess you've got enough stock suspension to handle it. Try the OEM spring helpers in place with your load at home first. It only takes 15 minutes to install them. (Maybe get a new set from Merlin if your's are older/ tired.) If this doesn't work, get some air bags. But on paper the OEM set up should really work. At any rate, I'd have to award you the die-hard super VX'er of the year award for all your enthusiastic use of your vehicle.