Re: Camper Package on F-350
stable loads are not a substitute for real springs, they just engage them earlier they don't add anything to the actual spring rate, so yes springs are the issue. just changing out the springs to the ones from a dually of that year will make a world of difference, you can also beef up the overload to one rated for a little more weight.
the V10 was a decent motor, but not decent enough to stick around, it had some inherent cam shaft oiling issue when they idled to long, we had them for work and 90% of the time they were idling 24/7, so we saw that problem haha
to me being 500lbs over isn't a big deal, some might think the sky is falling but as long as you compensate for it with the spring rate and such it would be fine. the actual weight handling of the axel is more than ford rates it for. so if you were to go to a spring shop, or if your a handy guy do it your self you would probably be happy with out spending money on a new truck, unless you just want a new truck.