I’ve done the linked procedure - all your recommendations are good, especially consistent method of filling the tank. For best results, average the calibration factor from multiple fill-ups. The procedure is only written to go from the factory default of 1000 to your custom number.For those that have hand calculated enough times and done so consistently, there is a way to modify/correct what your instrument panel display is providing for mpg's to align to your hand calculated numbers --> https://www.f150forum.com/f118/fix-inaccurate-mpg-display-2-minutes-421912/
I have not tried this myself yet, as my truck seems to be within 0.5 mpg of actual (At least when I am running summer diesel. On winter blend diesel I think the LOM (Lie-O-Meter) is off more.).
Before attempting the instructions in the above link, I would recommend tracking your calculations to display over several tanks. I would also fill up at the exact same fuel station and exact same pump number with the truck in the near exact position and fill up like The Fast Lane Truck guys do (wait until pump clicks off, wait 30 seconds, then fill again until it clicks off). Being consistent in approach will yield the most accurate hand calculated number to go in and adjust the LOM.
If anyone does try to re-program their truck with the instructions in the above link, please post your experience in doing so for the rest of us to learn from--thanks!
If you goof up your math or get bad results from the custom setting chosen, best to return to default and try things again after more data collection. It will never be 100% perfect, but my LOM is usually within a few tenths of my Fuelly calculation now, where it was off by over 1 MPG before.