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Buy a jug of kerosene to soak the carb's in and put a quality rebuild kit in it.
smaller intake= less hp = less gas consumed,unless its running rich or out of carb tune. Set the carb up to factory spec , something like 2 1/2 turns out from seated , so on and so fourth,then connect a vacuum gauge to the running motor and tune till its somewhere around 15 lbs, I forget, your manual will know.
your Truck sounds really cool, loose some weight from it ! sounds like your carrying a lot of crap!