The symptoms you have described occurred to me once before when I paid for someone to do a brake job on my truck. I had all 4 wheels done disc in front and drums on the rear. After a couple hundred miles it sound like crap when breaking. Brought it back to the shop and the mechanic and I took a test drive, He stated although it sounds like the front brakes is actually being caused by one of the rear drum brakes.
He took it back down and I replaced the drums with new ones and did not change the shoes. The problem went away. This happened on a 3/4 ton Chevy with 17 inch drums