I recently installed Add-A-Leafs from Autospring. They claim a +950lb payload increase and 1.5''-2" rear lift. I wrote a how to in my build thread but thought I'd post it here as well. First things first, place the truck in park, e-brake, and block the front wheels. Jack the rear axle up and support it with jack stands. Remove the tire. There are 4 nuts for the U bolts. Remove these. Air tools definitely help since the nuts have a thread locker on them. Remove the lower bolt on the shock. Now to remove the 2 centerpins holding the leaf pack together. It's a good idea to place 2 C-clamps on the leaf pack before doing so (which I forgot to do on the first side). If you're lucky you can use vise grips to grasp the heads of the centerpins underneath the leaf pack and remove the nuts. Mine, however, due to northern salty roads, were stuck on and trying to remove the nuts just results in the centerpins spinning with them even with vise grips. I talked to another member here and he has the same issue as well. You have 2 options. Take a torch and heat them up, or take a cut off wheel and split the nut in 2. I chose to split the nut. Cut down the center of the centerpin and nut. Now it's time to lower the rear axle on this side. This is where C-clamps are first useful because the leaf pack will spring apart the second the axle moves away. Leafs should be stacked according to size, with the longest on top. Also, the longer half of the leaf from the centerpin holes should face the rear. The Autospring leafs are sandwiched in between the bottom leaf and one above it. Lower the axle about 6-8" and remove the block (if you have a 4x4) Use the C-clamps to compress the leaf pack back together and install the 2 centerpins included with the kit. MAKE SURE THE LEAFS LINE UP STRAIGHT WITH EACH OTHER. ext add the block back ontop of the axle and jack the axle back up to the leaf pack. Make sure the centerpin heads seat themselves in the 2 holes in the block. Reinstall the U bolts and lower shock bolt, then tire. It's a good idea to retighten everything after 300 miles. Before, just over 8" of wheel gap. After, about 10" of gap
The more I use the truck since the AALs, the more I'm glad I did it. With all the crap I load in the bed each week, it seems to not sag AT ALL. Great when you have a front level.
Add 950lbs payload? hmmm.... I might look into this a little more, that would give me almsot 3800lbs!