Yep, what they all said. But I was sitting here trying to think of what it was back when I had cars and trucks with drum brakes up front. Back then it was somehow a brake was out of adjustment, or the front end had become out of alignment. Since those cars didn't have a warped discs or bad calipers or any of that, more times than not the shoes needed to be adjusted with the star adjuster at the bottom just like a drum rear brakes Squares have on them.
As a matter of a fact why don't you @Southern Eagle, '81's still had drums didn't they?, check your back drums and see if they need some evening up. And if not make sure your disc brake shoes are even. If they're not then you may have a hose problem back there to. I was braking just on the front for years and didn't even know it until I changed that rubber brake hose over the rear end and for the first time in years I could stop my truck like it should! It felt weird to have all my brakes working.