4 barrel LA Intake

I'm sorry but I don't believe a 5900 lb. 3/4 ton gasoline powered truck with 4.10 gears will ever get good gas mileage. If your lucky you'll gain 1-2 mpg installing a 4 barrel. Why did you remove the factory fuel injection? Fuel injection when working properly will get better gas mileage than a carb. 99.9% of the time

IMO the best thing you could do now is what others said about swapping the rearend for one with 3.55 gears. If you've got a granny low trans. you'll still have all the pulling power you would ever need. 3.55's should improve fuel mileage a lot more than a 4 barrel carb and you can easily change out a rearend just as quick as you could install a 4 barrel carb and get it tuned.