If it's the most powerful impact snapon sells it should have snapped the stud off by now. You probably have an air supply problem. Most cheap regs don't flow enough for impact wrenches. If your pressure gauge is dipping below 80, ditch the reg and run straight off the tank. The gun will survive 140psi w/o a problem.
It's the most powerful 1/2" gun you can buy, rather. Ala.. this guy: http://buy1.snapon.com/catalog/item.asp ... ir=catalog
And I wasn't cranking on it long enough to snap the stud off. I'm more careful than that haha. Running off a 60gal, 240V, 3hp tank, pretty sure i've got my reg set to 90psi. Might turn it up, but will get lower SCFM, so we'll see. Hadn't thought of that, honestly. It stands nicely in my utility room (where it's annoyingly loud to the wife... oops), and I don't pay much attention to it. In fact, I need to do an oil change on that pig one of these days.
Geek, I've never had a problem running everything I own (includes at least one of each of those things you've listed... save for powder coat guns and spray guns), without any hesitation or running out of air at any time. Granted, my tank might (read: probably) be excessive for a normal homeowner, so I dunno. My parents have a portable 20-30gal tank that gets killed with an impact gun or constant running of an angle die grinder. Gotta sit there and wait for it to fill back up before using for extended periods of time. The one thing I was absolutely having when I bought a house was a big ass compressor for all my toys. Pretty sure it was the first big purchase, haha.