The pick among the products tested is the Superchips Flashpaq Tuner. Its mileage-save tune took the 2001 Suburban to 18.78 MPG, almost 2 MPG clear of the same vehicle in stock trim, and it is the only device here that changes how the engine is actually fuelled rather than sitting alongside it. It was fitted on top of the MBRP High Flow Exhaust + Cold Air Intake, which is the better value at $448 for the exhaust: that system flowed 101 CFM against 74 for the 23-year-old original, dropped engine load 3 to 5% at cruise, lifted economy from just over 17 to 17.74 MPG, and cut the 0-60 time from 8.45 to 8.13 seconds.
The largest improvement of the whole program cost nothing at all. Raising tire pressure from 35 PSI to the 50 PSI sidewall maximum and easing the cruise back from 70 mph produced 20.39 MPG on the 2001 Suburban and 26.23 MPG on the 2020, roughly 3 MPG or 12.5% better than any other run on that vehicle. Stacked with the exhaust, intake and tune, the 2001 Suburban finished 22.4% better on fuel than the average of its first four round trips, and turned in its quickest 0-60 of the day at 8.01 seconds while doing it.
The gadgets are the other half of the story, and none of them stood up. The Obdiicats OBD2 Fuel Saver, Nitro OBD2 and 2G Fuel Saver Fins all returned less than the 17-plus MPG the 2001 Suburban managed with nothing fitted, and all three were slower to 60 mph than the stock vehicle, the Nitro OBD2 despite a claim of 35% more power and 25% more torque. On the 2020 Suburban the Eco OBD2 and NeoSocket Fuel Shark finished within a mile and a half per gallon of the untouched car, well inside what a single 77-mile loop can resolve, against label claims of 15% and 30% savings. In the generator, Ferox Fuel Additive Tablets and the Turbonator both ran shorter than untreated gasoline and left the combustion chamber carboned exactly as they found it. A tire gauge and a lighter right foot beat every one of them.