Tried to find answer unsuccessfully. Lift kits for most other manufacturers involve using blocks in the rear. I know they can also add shackles and/or leaf springs but in seems the goto method is basic lift blocks. But the Tundra when looking at the top several Suspension Websites seems to much prefer the shackles first and then add-a-leaf or new springs or even using both. Is there a reason blocks seem to be avoided with the Tundra. Both shackles and blocks have there pros/cons so simply not seeing why the shackles seem to be the way to go with the Tundra. I do see a couple of kits with the blocks but they are also of the cheaper variety.