2000 Chevy Silverado 1500: Brake pedal "gets stuck" or "locks up" on bumpy roads

I drive a 2000 Chevy 1500 with the 5.3l engine and 4wd. I do all my own work, but I’m slightly baffled by this one.

Driving on bumpy roads, specifically the ones around my house, the brake pedal gets stuck and I lose braking power. I’ve done a little googling but haven’t had any luck, and can’t really figure out how to word it.

Let me put it this way:
I’m driving, about 30 mph on a bumpy dirt road. Coming up to my turn, I start braking. Unfortunately, the worst bumps on the road are right before the stop sign.
Pressing down on the pedal, I feel a pop. Nothing major, I just feel something release. The brake pedal seems to move back with my foot as if I were releasing pressure. I try pressing the pedal back down harder, considering I’m about to barrel into the person on the other side at 30 mph, and the pedal does not move and I maintain coasting speed. It eventually releases (we’re probably talking quarter seconds here) and I manage to stop.

Does this all the time, and I’m so used to the roads I know when it’s coming, so I’m ready to stop. Still a pain in the ass, though. Sometimes, pressing and releasing the pedal multiple times as I come to a stop makes this less noticable and helps stop quicker. My buddy’s truck doesn’t do this. Why does my truck do this?