Surging 86 f-150

hey I got a 86 if-150 with a 300cu motor and a tfi intgition system I replace the carb, o2 and the map sensor and it still surges it idles fine but at speed it acts like I am dragging the brakes and the gas mileages is
down to 11 mpg .some time it will run fine and then it will start to surge. not sure if the new computer carb is at fault and is there a way I could replace the computer control carb with a noncomputer control carb .I need it to run better and nearly need the better gas mileages due to hurricane Ivan destroying my ford tempo . gas to work now is costing me over a 100 a week to go to work . thanks

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