When filling the old ram with fuel,would fill it all the way until it started running out. Had to replace two fuel gauges for doing that. Has anyone had that happen to them? Do you stop when the pump clicks off, with out topping the thing off? Seems some high volume pumps run so fast it suds the fuel and you can't get a good reading on the milage.

06 quad 4x2 slt cab high topper (what a beast)

 

I was reading here somewhere that to get the most accurate mileage is to fill the tank slowly until you can see the fuel in the neck.
Yes it's a PITA but seems to more accurate. There's also a mod for the tank that gives more capacity and takes less time to fill up.
https://dodgeforum.com/m_543398/tm.htm