With the spring only being an inch longer i dont see why you would need 3" or more... but then again im not a suspension guru. Atm im in the process of building 2" shackle lift and maybe 2.5" shackle lift. Gunna run an add a leaf with that to keep the truck level and from over-taxing the springs with the diesel in there. That is until i can do the SD spring swap in the front and Chev 3/4 ton springs, shackles and hanger in the back. Once the truck is leveled im looking for about 2-3" more lift, so i may very well try the stock SD spring first if i can get a deal on em. I cant see that a SD spring wont net any lift over ours, considering the differences in weight.