Front calipers are sticking. Had a leaking brake line fixed

First you have to determine if it's the front or rear brakes that are causing the problem. After driving for a few miles, feel the wheels to determine which ones are hot. If it's the rear, suspect a parking brake cable is rusted in the partially-applied position. If it's a front one, when the problem is occurring, stop on a slight incline, shift to neutral, place a block about a foot downhill of one tire so you don't look silly running after the car, then open the hydraulic system in various places to see where the pressurized brake fluid is being trapped. Start with the steel lines at the master cylinder. Loosen the soft metal nuts just enough to let the fluid pressure bleed off. You can also open the bleeder screws on the calipers to see if that lets them release.

Check that you have pedal clearance between the brake pedal push rod and the booster, you should be able to feed a few mm of free travel before the push rod takes up, look at this as well.

Since you have a replacement master cylinder, MPHAutos is right to look for pedal clearance. On some cars, most;y older imports, the push rod in the power booster is adjustable and if it's too long, it will hold the brakes partially applied. A misadjusted brake light switch can do that too.

If this was an older master cylinder and the brake fluid pressure releases when the lines are loosened at the master cylinder, brake fluid contaminated with a petroleum product is a real good suspect. That is a very expensive repair. Anything made of rubber will swell. The lip seals in the master cylinder will grow past the fluid return ports and block them. That will keep the brakes applied, then, as the linings heat up and that heat transfers into the fluid, the fluid will expand and put even more pressure on the system.