Rear brakes locking up....

[wyattglock]

I have totally rebuilt the brake system in my truck, except for the one freaking rubber hose on the rear. I am thinking that is going bad, but before I tear into them I wanted another opinion. When I first start the truck after sitting for a couple of hours, the rear brakes lock so hard they throw me forward in my seat. After 5 or 6 cycles of the pedal, the problem goes away and is fine until I let it sit again. I have bled them several times, and do not get any air out of them. Other than that hose, I can't come up with a reason why they are doing it. I am not losing gear fluid or brake fluid, so I can't say it is that causing the normal pressure problems. Any opinions are appreciated.