Hey guys new here I have looked everywhere for an answer but can find it maybe you all can help. When I'm driving the truck is doing fine it is a f150 4.6 4×4 but when I break it seams to lose power and when I slam on the breaks it compitly dies on me I have done a tune up changes the spark plugs have changed the wires done the oil change changed the fuel filter and also the air filter but it is still happening any ideas

 

Maybe the vacuum booster has a leak? Just guessing but the vacuum booster does use engine vacuum to boost the brake power. Maybe check the vacuum hose going to the booster.

 

I agree with Roadie, my gut goes to vacuum leak right away as well.

Is there an inertia fuel cut off switch in the kick panel passenger side? Maybe that's bad?
Not positive there is one in your truck, but for some reason i think there is.

 

Could be a sticky IAC.