Rear Brakes Dragging

[fordno1]

Working on a stock 1950 3100. Problem that is happening is the rear brakes are hanging, intermittently. At first, the left rear was hanging/dragging causing the drum to get hot. Right rear was fine. Adjusted the master cylinder push rod to have a little more free play. Drove it 5 miles and no issues. Ended up replacing the front wheel cylinders because fluid was leaking. Bled the brakes afterwords, drove it a mile came back and no issues. Customer picked up the truck and left. Returned 15 minutes later and said the right rear was dragging/hanging and it was hot to the touch, left rear was fine. Checked the e-brake and isn't hanging. Master cylinder, wheel cylinders, brake shoes were replaced prior to this happening. Any ideas???