27-30 mpg consistently, with 76000 miles on the clock. This is at 5500' elevation and higher. Before moving to Denver, I lived in Houston. At sea level, I pretty much saw 23-25 mpg regardless of the type of driving. More air means more horsepower, but greater drag and higher fuel consumption.
No drivetrain modifications, just consumables (fluids, filters, belts, plugs, wires, O2 sensors
).
