Best way to improve Gas Mileage and Comfort in 1992 F150?

I have a 1992 Ford F150 Supercab Automatic with an 300 Inline 6. Rear Wheel Drive. Currently the truck is completely stock.

In the distant future I plan on rebuilding the Engine and Transmission and taking me and my girl around the US for a year or so. I have no plans on offroading other than camp / RV sites.

I'm wanting to get the most mileage and softest suspension I can. The only thing is I want to keep the Inline 6.

So, basically what would you guys do to the truck?

Talking Transmission, Differential, Turbo / Supercharger, etc.

I plan on installing a camper shell, upgrading suspension so I can have about a ton in the bed. Replacing AC compressor with electric, replace clutch fan wirh electric, and installing another alternator and batteries.

Thank You!

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