Truck runs but dies when I drive it down the street. HELP!

I think the first place to start would be the Carburettor. I would suggest an overhaul / strip and clean. You have probabaly got 'dirty' or residue being brought up from the gas tank so change the filter aswell.

It could be a vacuum line issue, especially if it's when you hit the brakes. The power brake booster (if it even has power brakes) takes almost all the vacuum from the engine when you hit the brake pedal, if you have a dryrotted vacuum line, that will cause a lost in vacuum and the engine will die out. Put a vacuum gauge or tester on the truck, it should have 14 inches of vacuum at all times when it's running. If it takes 20 minutes before it starts again, then you might have another problem with the starter. If it doesn't even crank over or cranks real slow when the engine is warmed up then the starter is probably starting to go too and when it gets hot , it doesn't work until it cools off. .If the truck has been sitting and not driven very much, the gas in the tank turns gummy and will clog up a carb in no time at all plus other components start to wearout quickly once you start using the truck. You are probably driving the truck more often than your grandpa and that's when stuff starts going wrong after sitting for a long period of time. You're probably going to have to start replacing a lot of parts the more you drive it. Parts tend to dryrot, rust or corred when not used daily. Unfortunately, that's what happens with older vehicles when they sit idle for long periods of time and then all of a sudden get used on a daily basis. Good Luck, Kenny.