The brakes go all the way to the floor. It will stop the truck eventually but you have to step on it hard. Brakes will not pump up at all. They will pump up when the truck is turned off but go to the floor when its started. The ABS and brake light are both on. I topped off the fluid but still no pressure. Master Cylinder maybe? If not where would the most common leaks be?

 

Brake line running in the frame next to gas tank.

 

i'm trying to decide whether you have bad master cylinder or a booster problem.

assuming you have no leaks in the lines, wheel cylinders, hoses, or calipers, and no loss of fluid - then the main pressure producer is the master cylinder. when it goes bad, the pedal will go to the floor - maybe s-l-o-w-l-y while sitting at a red light, maybe rapidly, as in oh-****. usually, pressure will improve with several pumps and provide you some temporary stopping power. and finally, a master cylinder usually goes bad slowly over time, and give you that soft pedal warning for awhile.

the booster is a mysterious (to me) device. if the diaphram is bad.... i don't know. you need more advice than i can give.
http://auto.howstuffworks.com/auto-p...ower-brake.htm

 

I heard that you can check the booster by pumping the brakes with the engine off, the pedal should get harder to push down each time.
then while keeping pressure on the pedal you start the engine and it should get softer and move to the floor a bit. If it doesn't firm up while the engine is off the booster is bad.

Other than that + one on the line above gas tank on drivers side.
EDIT I guess I should have read again, the OP seems to have done the booster test. I'm celebrating New Years early.... Hicup...