Hi, I have a 1987 D150 pickup with a 318 and 904 transmission. It sits at about 3500 rpm at 65mph. Kills the gas mileage. I want to keep engine and tranny the same, but is there possibly a better rear end to use to lower my rpms, and/or other mods to help mileage. Thanks

 

You can change the differential to higher gears if you want and it will improve mileage slightly. There is a trade off in lower towing and hauling ability and more wear and tear around town. Why do you own a truck? Is it only a high way truck? These are the questions that only you personally can answer.

First figure out what gears you have. You can take the vin to the dealer and get a build sheet for your truck if you think it is stock. There should also be a tag on the pumpkin bolts with that info.

 

Another thing can affect is tires/wheels. If you have big tires/wheels and are heavy. On tires the ply rating can be more and will be a heaver tires