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Congrats on living rent free...
I don't believe they're any special tips regarding driving on gravel.
If it were me, I would buy a Scan Gauge or Ultra Gauge if you do not already own one. They are much better than the factory mpg gauges if your vehicle comes with one. The reason they're better is that they give instantaneous feed back not just a average, which will allow you to find the best speed or rpm for maximum mpg. Usually just as the transmission shifts into high gear or lock up.
Find the sweet spot on the gravel and keep it there.
Other than that, just read
100+ Hypermiling / ecodriving tips & tactics for better mpg - EcoModder.com
and
65+ Vehicle modifications for better fuel economy - EcoModder.com.
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