Chevy C15 Break Troubles

Have a 93' C15 1/2 ton P/U; 4.3 6 cyl engine.

Break light on dash came on and started flashing. 4 short flashes then one long. Kept repeating the same flashing pattern. Plus, was getting real "mushy" on the peddle. So, changed the Master Break Cylinder. Seemed to help. Break light stopped flashing and now just stays on. Break pads, front and rear, look ok.

Any suggestions as to what might be going on?

Thanks in advance for any help.