Key Wont Turn Ignition 2000 Gmc Sierra

[Big5]

I've been having an intermitant problem with the key in my 2000 GMC Sierra not turn the ignition. I can put the key in 100 times and try to turn it and it won't turn. Then after 20-30 minutes it will all of the sudden turn over. This has nothing to do with the steering wheel being locked in an angle. The problem will happen about every month or so. It's really getting annoying. The last time it happened I was stuck for about 40 minutes jamming the key in and out of the ignition trying to get it to turn. Then all of the sudden it turns. Is this an ignition switch problem or a tumbler issue or something else? Any suggestions would be appreciated.

[Fortune50]

Either a problem w/ the key or w/ the lock cylinder. Do you have any other keys to try? If they don't do any better, then probably have a bad lock cylinder.