I have had this problem in the winters for 2 years. I don't think it happens in the summer at all. Every once in a while when the truck is cold (if it sits outside on a really cold night), the brakes are very hard, and don't stop the truck. For example, yesterday I was backing out of the drive way and mashed the brakes all the way down and there was almost nothing. They were hard right away, but no stopping going on. I kept pumping them as I was backing up and then they seemed to catch. No problems after that.

I just installed new rotors, pads, shoes and drums. What gives? New master cylinder?

thanks