I had the same problem, and I had to remove the hub and pry it out of the wheel. Once it was off, I cleaned the hub area well. Still, the next time it still wouldn't come off, but I found I could pry between the drum and wheel on the backside with a 3ft. prybar. Las Schwab has lots of tricks for big trucks and tractor tires, I talked to the guy there, but he said it might cost $60+ and he still couldn't guarantee it would come off. They have wheel jacks and stuff that works a lot like a jack turned on its side. Driving with the lugs loose seems like a good way to mar the threads.
