Yup...clean threads are the way to go! Out at the wrecking yard a couple weekends ago, I would've been able to get a couple of decent Chevy Sport chrome wheels, if the PO of that truck had bothered to clean the studs occasionally. I could only get them partway loose even with my cordless impact gun, ran the battery down on it trying, and tried with my long lug wrench too. I was bending the handle, pulling on it with all my weight....
On the two trucks with the alloys, only problem I had getting the wheels off was the left rear one that got caught up in the axle hub and studs. All those nuts broke loose fine, could spin em off by hand.
I generally use a wire brush on the threads, when I have a wheel off for service.