We aren't huge fans of big lift blocks thatgo under leaf springs on top of axle spring pads, and Off Road Design not only agrees but has a better option with what they call a Zero Rate add-a-leaf. This steel shorty leaf gives a 1-inch lift without the ill effects of a tall block, allowing the use of flatter, more flexible springs while still gaining clearance for taller tires.
This install is easiest with the springs out of the truck, but can be done with the truck frame on jackstands and the axle removed. Before you drop the axle, look at the U-bolts and determine if you have enough thread for the new 1-inch-thick leaves. With the pack out, clamp the spring and remove the center pin. A kit of add-a-leaves retails for $40.
The Zero Rate add-a-leaf is not really a regular block, because it is actually bolted directly to the leaf pack with a new longer center pin. Thus it doesn't have the possibility of popping out or breaking like blocks do. Since it is only an inch tall it doesn't add considerable leverage to the spring pack like bigger blocks do. It also has the added bonus of allowing the installer the option of moving the axle offset 1 or 1 1/2 inches from center in order to gain more tire clearance. To offset the axle, simply use the supplied bolts in one of the recessed holes as your new center pin, and then cut the new center pin to an inch in length, and run it in the center hole where it will still engage the spring pad. Remember to always install the leaf with the rounded edges up.