why does my pickup die at idle and has no power

check ignition timing, vacuum pressure and fuel pressure. Just replacing parts is a gamble.

It's most likely losing fuel one way or another, either the float was never adjusted properly (if Carb was rebuilt) or is stuck or it may be that the grade is enough to be considered a carburetors "downfall". Basically stock carburetors can handle only so much of a grade and still supply fuel.