Rear Tire Locks up while driving

I was hoping someone may have had or heard of someone having this problem. I have a 97 K1500 with 140,000 miles. Last winter while trying to back out of a parking spot my left rear tire locked up without me hitting the brakes. Once I put my foot on the brakes and pulled forward everything worked fine. It did this again about 6 months later and just did it again this weekend. I thought one time may have been a fluke. I should have looked at it after the second time but I never got around to it. But now that it has happened 3 times I need to look into where the problem lies. I am hoping it is something in the brakes that is causing the problem however when it locks up the wheel does not move at all. I am hoping it is not in the rear end but it could be.
I plan on pulling off the back wheel to look at it and start there. If anyone is familiar with this situation please let me know so I am not on a wild goose chase.
Thanks

Pull the drums and look for any moisture. If the axle seals are leaking, they need to be replaced. Usually, when an axle leaks, the brakes lock up when you apply the brakes.

In your case, I suspect a bad brake spring. Ask for a "Combi" kit at the parts store to get all the springs for the rear brakes.

//2000CAYukon

Most likely your rear brake cylinders, that's what mine was when I replaced them not too long ago. If it was your spring's you'd notice that the rear brakes are hardly working at all and when you pump the pedal it'd feel like you have air in the lines, but I just went ahead and replaced the rear cylinders, springs, and shoes all at the same time. Cylinders ran me about 45 bucks a piece, and I can't remember cost for springs, wasn't too much though.