WDH question - do I need to purchase a different shank?

I'll buck the system. yes you need a lower drop. You are starting out an inch too high. Once you adjust the WDH correctly. You will be an inch too high, Especially if you have oversized springs, you may even be higher.

Remember the goal of a WDH is to return lost weight to the front of the truck. Do that, and the rear will take care of itself. but if it already too high. It will remain so.