[Bluestep]

1982, you didn't provide any information about your vehicle. So generically speaking you need to check to see what has been modified on your rig. Does it have all the vacuum hoses hooked up correctly, does it have an aftermarket carburetor(s) (which is most likely set up rich), is the timing set correctly, has the advance curve been optimized? Check and repair or adjust all of those things and then do what you can to make the vehicle roll easier. That would include taking extra weight out of the vehicle (tools, tire chains, etc.), make sure the tires are properly inflated and are not overly wide. Check the gear ratio of the rear axle and if it is low (numerically high) will have a huge effect on mileage. You can help the gear ratio with a change in tire size (if it is too low use as tall a tire as is practicable, and correct the speedometer)

If it still has the Quadrajet carburetor it can be tuned to be very efficient.

After all the tune up has been optimized your driving skills need to be optimized for fuel efficiency.

After all of that you will still not have a vehicle that was designed for fuel efficiency, but it will be a cheap to maintain, useful vehicle. Economy isn't about just fuel mileage.