Problems W/Mobs Constantly Causing My Pulverize to be Unuseable Until I Click Other Abilities

So I get positioned to Pulverize a bunch of mobs & they grey out my Pulverize until I use Claw or my heal usually. So I have to get closer to the mobs to use claw, which totally hoses my pulverize. This is happening constantly, to the point where the build has lost all fun. Any ideas?