Brake lockup

Got in my Jeep this morning and after putting the tranny in reverse, let off the brake and push on the gas, and nothing. Put the tranny in drive, let off the brake, pushed the gas and again nothing. Got out looking for something under the tires. Nothing under any of them. Got back in, put the tranny in reverse, let off the brake push on the gas and still nothing. Push the gas a little harder and get a loud pop from the rear axle, and the jeep moves. Pull out of the garage, and hit the brakes and get a grinding sound. Back up a bit farther and hit the brakes and they sound fine.
Didn't really want to drive it, but with freezing rain coming down I decided to chance it. Everything was fine on the ride to work and then the ride home.
Any thoughts on what might be the problem. This is the first time this has happened. It did sit for about 2 weeks prior to this morning.
It's any 88 4.0, AW4 and NP242 with a d35 and drum brakes. TIA

Rust or ice, whatever it is, but it happens and nothing to worry about.

Take off the rear drums and make sure nothing is snapped off like a retainer spring or something like that. Where you said there was a loud pop, I would put the back in the air, remove rear axle cover and spin it to make sure that nothing is out of whack, like a chipped gear tooth or bad bearing causing it to move and bind. Just a couple ideas to check out.

What did it feel like when you heard the 'pop'?
I'd almost bet on rust/ice. Especially if you didn't have any strange behavior or sounds after the initial. Still, you'd better pull at least those wheels and drums just to be sure.

My '92 has been mostly off the road for two years, and every time I move it, there's a surprise! The rear drums like to rust up and seize just like you've described, but they're ok after a few blocks. If they quiet down and behave normally after a little bit, you should be alright.

Thanks guys. Was kind of thinking it might have been some rust in there, just needed some backup on that theory. Will try and pull the wheels off this weekend and take a look just to be sure though.

Wet brake shoes will freeze to the brake drums if you leave your parking brake on over night.