I recently purchased a 2006 F-250 with a 4" lift on the front. After inspecting it, I discovered the back is sitting just under an inch lower than the front. So I want to lift the back, so in looking at adding a leaf spring in the back they have two, one set is a 1 inch lift the other is 2 inch. But I am sure with everything they do not give a true 1 or 2 inch lift. Which should I go with?