Coming home from the Sierra's this weekend (down hill on a mountain road) I noticed my brakes seemed to be getting soft, I pulled over to check my brakes and once stopped my pedal was mushing to the floor. If I pumped the brakes I would regain pressure. My fluids were fine with no signs of leakage under the truck. I continued down the moutain in low gears and pumping the brakes as needed until i reached a town. I stopped and checked everything again and all appreared normal and the brakes seemed to be working properly again. I never saw any idiot lights on the instrument panel during the failure. Any ideas? If the master cylinder was bad wouldn't the fluid leak?

Sounds eerily similar to this post where they replaced the master cylinder:

http://www.tundrasolutions.com/forums/brakes/215456-common-piston-or-master-cylinder-problem/

Maybe overheated them? How are they now?

Chances are you just over heated them...brake fluid is designed to withstand boiling but slowing a big truck down a mountain can surpass even the temps at which brake fluid boils. This can be avoided by making sure you have fresh fluid (reason you change brake fluid is because it is hygroscopic which means it absorbs water) as well as fresh brake pads and rotors that arent worn past their limits.

Thanks for the responses. Overheating seems to be the concensus. I did neglect to mention I carry a Four Wheel Pop Up Camper which would exacerbate the problem.

Everything has been normal since then, I took it in and had the system pressure checked (ruling out the master cylinder) and then had a system flush with new fluid added. I feel comfortable that the issue is resolved.

Also make sure your rear brakes are adjusted up properly. The auto adjusters never really work. Then all your braking is done on the front and that is extra hard on it.

You need to replace the factory brakes with some aftermarket parts if you want increased braking power and since you tow you should invest if you plan on keeping the truck. You should also check the rear, not just the shoe clearance but the brake proportioning valve and make sure it is set to 4.72" bolt center to bolt center. I had to correct mine as it was way off from the factory.

If you do a lot of towing, look into an aftermarket pad with a higher heat threshold that can handle repetitive braking, dot 4 brake fluid, and maybe even stainless lines. I like the HAWK LTS for daily use, and the HAWK SD for heavier duty use. A Russell line kit makes a big difference in pedal feel as well, and really tightens up the mushyness.

Does your pup have trailer brakes? Would really help.

If you do a lot of towing, look into an aftermarket pad with a higher heat threshold that can handle repetitive braking, dot 4 brake fluid, and maybe even stainless lines. I like the HAWK LTS for daily use, and the HAWK SD for heavier duty use. A Russell line kit makes a big difference in pedal feel as well, and really tightens up the mushyness.

Where would one find the Russell line kit? Are those braided lines? Are the lines and pads available online? Thanks. I tow (something, loaded down utility trailer, 5th wheel you names it) quite frequently and do not like the mushy pedal feel. Reminds me of the 90's models GM trucks

yes sir, all online.

Russell Stainless Steel Brake Line Kit | AJUSA.com (http://www.ajusa.com/Russell-Stainless-Steel-Brake-Line-Kit-c2895.html)