Tell us what it is that you're wanting to do with your truck. Perhaps then we can be a bit more specific with help.
You have an F-250. No matter what you do to the rear suspension it will still be an F-250, and registered as an F-250, with an F-250 load limit, regardless of it's upgraded ability. I believe there is more than the rear suspension which goes into making it an F-250.
I have an F-250HD which I used to haul a big old cabover camper. The weight of the camper dropped the rear end several inches, and it swayed enough to make me nervous and uncomfortable. I considered it marginal on safety. I added a pair of Helwig 2500 pound overload springs to the rear. It rode level with the camper, and swayed less, but still swayed some. BUT, I still had an F-250, and was legally limited to an F-250's weight specifications. Without the weight of the camper in the rear, that truck rode like a proverbially truck. The rear end was very stiff.
I ultimately solved that problem by getting and F-350 Dually. It handles the weight of the camper so much better it's unbelievable.