[truckin 79]

All good advice here I would also throw in that maybe the wheel cylinders are the problem. I dont know why other shop could not locate the correct ones but there is a reason your truck had those wheel cylinders. I bet the new cylinders are pushing the shoes out to much where the old ones probably collapsed down further in the wheel cylinder. I would look up on online your self and try and find correct wheel cylinders for your truck. I recently replaced shoes, drums and wheel cylinders. The parts store only listed on set of WC but turns out there are 2 different ones for a 79 heavy half. Good Luck