One thing that I have is a CarChip - Davis; a Black Box that will record your MPH, and four engine perameters, such a engine Temp, Battery Volts, O2 Voltages, Manifold Pressure. It will show how well the cruse control will keep your MPH up, level, but will keep you under the Radar range. My son, in the ARMY was having problems, emissions. The dealer could or would not find it. Sent him this device while he was in Hawaii. It showed the temp at 150 F. New Thermostat was a quick, cheap fix. Everything is imported out there. Gas is expensive, however there is nowhere to go.
The second trick I have come upon. When stopping for gas, ask folks how they are doing. Tricks they have found.
Diesel will give you great mileage, If you engine is Diesel. Once in a while you will hear of some one wanting to get in on the action. It is one thing that you do NOT want to even Think about.
Topping OFF the tank. A NO NO. Raw gas getting into the CAT may kill it. And if the engine will not get the O2 reading to adjust the fuel flow. Just let the pump shut its' self off. It is of little advantage to squeze it.