That will be the best way to measure the real world fuel consumption. While it's really rare to drive that far for the sake of finding the consumption. The full tank of fuel for the usual route will do for most. I do reset my accumulated drive after every refuel. Keep an eye on my consumption. I usually get between 24-29 MPG for my 3.3 which is very good even though my daily commute is around 75% highway.Seeing 27-28 highway with the 3.3 , around 21 mixed city/highway [which means upper teens city]. I always turn off the stop/start when I get in, so the 1 MPG that might afford me isn't reflected in that number.
I'd like to see a LONG roadtrip that consumes a full tank of gas, returning over the same roadway (to account for any elevation and wind change/loss in either direction), at the same speeds. 37MPG isn't realistic for the 2.5L , the 31.5 MPG result is closer to reality. None of the car computers do a good job estimating on only 3-4 gallons of fuel. They need a healthy sample size to be at least ballpark close.
I've been doing a lot of long highway trips for work. So for 3300 miles since new, I'm at a lifetime average of 27.4 mpg. It's not unusual for it to be in the mid 20's for city and fun driving though.My 2.5T gets almost 23 mixed. I must really be letting it eat compared to you guys lol