Right side Rustys leaf is saggy

My right side leaf pack is sagging pretty bad. It sits about 1.5" lower than the left. Has anybody ever added an extra leaf to just one side? Or am I pretty much SOL and need to buy 2 new packs?

Personally, I wouldn't even consider adding a leaf to just one side. For that matter, I'd probably buy a new set of rear leaves.

How old are these springs?

Swap leafs side to side, the other one will sag eventually too. Then, when they're both sagged... buy a good pair of leaf springs (ie, not Rusty's) to replace them.

The drivetrain rotates clockwise (from the vantage point of the driver's seat), thus the natural "torque lean" effects the passenger side rear spring the most... taking off from a dead stop compresses that leaf the most, and over time they sag, especially cheaper leaf springs.

This is very common, just swap the leaf packs side to side as "NotMatt" suggested. Even Deaver or Alcan will have the same issue after a while.

This happened to me, I called Rusty. He sent me an add a leaf for that side, didn't seam like it rode or flexed any different after I added it.

I've had it happen a few times. I just added an extra leaf to that side. I've had quite a few homemade leaf packs, before people started call them "bastard packs". All of mine had one or two more leaves on the right side than the left side, never could tell the difference side to side.

Swap sides, or get new springs, but there's nothing negative about adding another leaf.