I have an 84 ford f-150, and when at stop lights it cuts off when i step on brakes. i changed fuel filter, master cylinder, and power booster and still have the problem.

Are you sure it's brake related or is it cutting out when hot? If you start it up cold, let it idle and hit the brake is it dying out like that as well?

It dies out when its placed in drive or reverse. whether its hot or cold, it does the same thing. At lights, i have to put it in park, or neutral to keep it from shutting off.

Is your idle too low?

I turned up the idle and it is still doing the same thing.

I would try and replace your transmission vacuum actuator. Also check all of your vac lines.