bad gas mileage

I have a 1999 blazer 4x4 i am only getting about 150 miles on a tank of gas with averages to about 10 miles a gallon is there anything i can do to get it up higher. Its just as bad as my 1983 chevy truck 4x4 which has a 350 in it.

whats the mileage and what repairs have been done recently?

since i purchased the truck 3 months ago w/ 105,000 i have had to rebuild the engine new wires, plugs, water pump, intake gasket, rotor, O2 sensor on left bank pretty much the person who i bought it from covered the engine knock up by using lucas oil.