I don't understand the math either. Assuming a 3000 miles one way trip, 6000 miles round trip. IF you average 10 MPG (to make the math easy), it will take 600 gallons.
At $3/gal, it will cost $1800
At $2.3/gal it will cost $1380. - a savings of $420 on the total trip.
Having said that, I put about 30k miles a year in my coach and an app called "Fuelbook" that was developed for truckers. You put in your destination , it finds the route, and gives you the 10 lowest prices for diesel along the route that are within 1 mile of the route. All of the locations have truck lanes - this is a huge benefit for me over GasBuddy.
The only issue I have with the app is that it doesn't seem to include Flying J's. Not a big deal to me since they're usually high priced anyway, but I like to stop at them occasionally when I need to get propane.