Originally Posted by mds47588

At one time it was generally accepted that driving on a trip with the tailgate down would get ya better mileage (70's & 80's) but as trucks have evolved and gotten more aerodynamic and refined it's now regarded as driving with the tailgate up will get you more mileage. Today I had started a looong road-trip (approx. 1,100 miles and I decided to try this out. Of course nothing was in the bed and 99%+ driving would be interstate.

Truck is the one in my sig currently with 190K miles in a good state of tune using 87 octane fuel.

Tank 1: From Picayune MS to Rising Fawn GA was 405 miles. I got on the interstate at 4:50am and traffic was little to non-existent. Cruise control was steady at 75mph w/light rain falling. 16.1 mpg.

Tank 2: From Rising Fawn to Natural Bridge VA was 421 miles. Again light rain, cruise was steady (mostly) at 70-75 mph. Heavy traffic thru Knoxville and for a good portion on I-81. In fact, if the tailgate was left up, I am sure that this tank would have been worse than the previous account all of the accelerating and braking...etc. I was shocked to see 17.56 mpg. Nearly a 1.5 mpg gain under less than ideal conditions.

I filled up again at Natural Bridge and will fill up one more time before I'm off the interstate tomorrow and get a more accurate number as tank 2 had the potential to be even more.

This is my truck's mileage. No two will be the same and I'm sure that numbers will would be all over comparing it to a Chevy/GMC or Dodge...etc.