Choke Problem?

I have an 86 gmc 1/2 4x4 305,77,000 when I start up in the cold mornings it acts like the choke is not working it just idles speeds up very little,then when it is time to leave it seams ok but 1/2 a mile or so down the road it acts like the choke is stuck! it loose all power even the brakes become hard as a rock? Barley run very sluggish! Lost vacuum, But when it time to go back home and it is warm outside its better! Ive tried gummout for the carb and choke it didnt work,checked all of my lines they seam to be ok! Air Filter ect! Any suggestions Out there!
any help would be very Appreciated ! Thanks Rocker