I just noticed my saw has the same movement. I figured I could just tighten the center bolt. But I guess you say that don't work. Is there a shim or washer under the rotating portion that can be removed or ground down?
In my experience, using extensions always lessens the torque on any impact, air or cordless. the more extension you have, the more it absorbs the hammer action. are you using solid 1/2" drive extensions?
its not really a clutch. its a spring loaded hammer mechanism. when enough pressure is encountered, the hammer rises, turns, and impacts. if its not hammering, is it stalling? any grease should work inside it.