MPG Motor Magnum vs. Hemi

With .008, you may be walking a thin line between the engine barely surviving and self destructing. The exhaust valve needs seat time to shed heat. And if the valves don't fully close, there goes your cylinder pressure and MPGs along with it.
You might be able to get a grip on this with a vacuum reading at say 100*F and compare it to when fully warmed up. I have never had to do this so I'm just tossing out ideas. I know my slanty told me it wanted more clearance when I did this, and the idle improved remarkably.