not sure how nice your springs are, but adding a leaf will limit flex, adding a block will only procrastinate your problem. Blocks multiply the torque on the leaf springs, so they will wear out even faster, not to mention axle wrap and the fact that blocks can shear. A the bigger the block the worse of couse.
After using a block myself cuz it was cheap, and having ridden in trucks with an add a leaf I finally broke down and spent money on custom springs.
I would say you might take out one of your leaves to trade for another, but there are springs that will give 8" or more lift that are not custom. You might look at a drop hangar, or custom springs. Be ware of blocks and long shackles that give you a bad angle!
and the final chapter is I put a 7" rear leaf to go with my 5" front spring. I really like how it looks!
hope this helps