[ecomodded]

The route and passenger weight may of played a part perhaps your driving style changes slightly while carpooling or your tires need air, pump up to max sidewall pressure and coast more often with your carpooling passengers.

Also fill to a level on the filler tube and use that level for all your fill ups, also use the same gas station and stall.

I squeeze near a gallon into my tank after the auto fill has stopped and always fill to the same height in the filler tube. To empty before refilling I drive 75km after the low gas warning light comes on to maintain continuity with fill ups