I'm pretty sure the heaviest 10.25 axle rating is 7400#.
Not clear exactly what you're trying to do - but you probably want to start with a truck that's rated for the weight you plan to haul. Putting heavier axles under a light truck *does not* mean any of the rest of the truck can handle higher loads. Frame and suspension would be my biggest worries. Plus the legal GVW would still be the original weight, so you'd be legally overloaded.......
