There are a number of ways to increase load capacity. The most functional way is to add leafs to your springs. air shocks is another way although when you get up unto the capacities your in, that's not a good option. There are speciality spring shops around that will rebuild your springs, adding a leaf. as far as the actual increase in capacity, they would have to tell you that because they are the only ones to know what was being added and what the benefit would be.