Chevrolet Repair: 1990 chevy, diesel ,p30 truck, chevy diesel, two wheels

Question
After driving a few miles I notice that the brake pedal does not go down as usual it brakes with a slight touch. It gets worse in the next few minutes until it locks up completely. In other words I can't drive the truck because the brake is being applied on it's own. After a while it goes back to normal. This has happened twice to me and I was lucky to be close to my house so I could drive home, but I had to press the accelerator all the way down and drive about 5 m.p.h. and the engine overheating. A few years ago I had a similar problem when one brake was constantly braking, not to the extend that I couldn't drive, and I replaced the hose that runs to the caliper and that solved the problem.  This time the problem seems different.  It feels like both brakes are gripping tightly the wheel, not just, not letting go. Also the difference from previous time is that now it is normal after I waited a while with the engine shut off, but previously it didn't make a difference, it was constantly slightly braking. After it happened the first time that the brakes completely locked up I checked the fluid level in the master cylinder and it was not full, so I filled it up, but it happened again after driving about 10 miles.

Answer
HI ISAAC, FIRST THINGS FIRST..I WOULD LIKE YOU TO DRIVE THIS TRUCK UP AND DOWN YOUR STREET UNTILL THE BRAKES FEELS LIKE THEY ARE LOCKING UP AS YOU SAY..THEN JACK THE TRUCK UP AND LEAVE IT IN NEUTRAL, NOW SPIN EACH WHEEL AND SEE WHICH ONE IS LOCKED UP..IF ALL 4 ARE LOCKED UP THIS SOUNDS LIKE THE MASTER CYLINDER MAYBE NOT RELEASING ALL THE WAY.STICKY PEDAL OR PUSH ROD STICKING. TRY PULLING UP ON THE PEDAL SLIGHTLY AND SEE IF THIS CURES IT. BUT I THINK YOU WILL FIND ONE OR TWO WHEELS THAT IS LOCKING UP CAUSING THIS..SO IF YOU FIND IT IS ONE OR TWO WHEELS THAT ARE LOCKING UP LOOSEN THE BLEEDER SCREW AND SEE IT THIS RELEASES THE BRAKE ,IF SO, THE HOSE MAYBE COLLAPSED NOT RELEASING THE PRESSURE. IF THIS DOES NOT FREE IT UP THEN THE CALIPER IS NOT RELEASING [IF ON THE FRONT]TIME FOR A NEW CALIPER. IF ON THE REAR,, THE WHEEL CYLINDER IS LOCKING UP..TIME FOR A NEW WHL CYL. THIS COULD ALSO HAVE A PROBLEM WITH THE PARKING BRAKES STICKING..BAD CABLES [RUSTY]. THE FACT THAT THIS HAPPENS AFTER YOU DRIVE IT A BIT SOUNDS LIKE THINGS ARE WARMING UP WHICH WILL EXPAND THINGS FAST AND LOCK UP FROM THE HEAT OF FRICTION..LET ME KONW HOW YOU MAKE OUT.GOOD LUCK,,,TOM.