Pros of an Add-a-Leaf over a block: Add-a-leafs increase load capacity (though still not your GVWR), aren't prone to axle wrap like larger blocks, and can be combined with larger blocks to fine-tune rear ride height if needed. Cons of an add-a-leaf over a rear block: stiffer rear ride quality (though that can mitigated with aftermarket shocks), more difficult installation, and they start out at about 2" of rear lift before settling to 1.5" which can give your truck a pretty stinkbug look until they're broken in.