Sorry to hear that you are more patient than me . Been there done that I am at the point now where I hope it burns on the side of the highway. Same problem twice already. Took all the fun out of ownership.
I would install a fuel flow meter ,
I would install a fuel flow meter and once on the highway at a steady speed hit reset and go to the calculation of 6 pounds or 1 gallon and clock your mileage they are very easy to install