Shim stacks are $40, and the labor shouldn't be more than $100 per shock. Although shipping and install removal are probably similar. Still shouldn't be 2 grand. However, as several people have said, if this is your problem King screwed up big time building your shocks and you have the wrong part.
That said, check your part number with King and make sure they send you the right thing, should be on the tag that came wired to the shock. Also make sure they charged the shock before shipping.
You can do an easy test of shock pressure by jacking up the back end of the truck, and un-bolting the bottom of the shock from the axle. If you can easily push the shaft back into the shock, there is no pressure and that's your problem. If you have to really work at it, or cant compress the shock by hand, then its properly pressurized.
Assuming you have shock pressure, I'd check the other issues mentioned up thread before jumping to re-valving shocks. For a close to stock weight truck, and close to stock height King has their shit together. The only other thing I'd check is to make sure your problem isn't down travel, that is that your "bang" isn't the suspension bottoming out before it can hit the bottom of the hole you went over.
Once you're sure it's not suspension travel related, then I'd look at shock valving. Down South Motor Sports or Filthy motor sports are the go-to guys for this. King can do it, but they take forever...
