350/3500 srw crew cab long beds 4wd diesel trucks with those big 4xxx lb gvwr based payloads if all placed in the bed over the trucks rear axle may overload the truck 7000 rawr. I've seen some owners of trucks this size say their truck unladin rear axle weight was in the 3400-3500 lbs range leaving 3500-3600 lbs for a max rear axle payload.
Best to weigh the rig on a scale that way actual loads on the trucks axles/tires/suspension are known. A upgraded in those components can then be addressed ...if needed.
