How improve fuel economy

460? A higher gear ratio would help if you have stump puller gears.

If you see a big reduction in gas mileage you may be due for a tune up and clean or replace filters. Clean throttle body and intake ducts and intake air sensors and all that. If you know for certain engine is running well, and still have poor economy, look at the clutch (torque converter clutch or TCC), or manual clutch, if it's getting worn it can be slipping in higher gears. You didn't say what engine/trans you have so I'm just putting a few generic suggestions out there. A band in the tranny can be slipping as well. Loss of MPG can be something to do with the engine itself, worn valves or loss of compression, etc. You can try some tests for those - compression, leak down, power balance, exhaust leaks, and so on. I mean the list of things that can cause loss of MPG is pretty extensive, even a vacuum leak can do it. Start by looking for any OBD1 trouble codes by counting blinks of CEL.

Watch your driving. smooth, steady starts, pay attention to traffic signals ahead and coast to slow down and not need to hit the brake so much. This also helps to "Make" the light as it turns green if no one is ahead of you. 30 years ago we didn't worry much about mpg. My 82 Olds 98 averaged about 10 mpg. No computers, valve timing etc to improve milage.