Thorny brake problem

My 97 chevy 1500 p.u. has 101,000 miles.

3 mos. ago while backing up the brakes

locked up. I couldn’t go either way!

When I shut it off for a few mins. and

restart I can usually resume backing up,

but then it happens again! It never occurs

in forward. The last time it happened I

pressed the parking brake down and released

it twice and I could move again. It happens

when first using it mornings, so Iv’e been

backing into my carport so I don’t have to

back up the next a.m.

Any help would be appreciated.

Do the brakes lock up by themselves? Or do they lock up when you touch the brake pedal?

And are these drum brakes?