Thanks. Your mpg certainly seems low compared to others with 4WD and 3.21 gears. The Hwy mpg suffers at speeds over 65. I would think 19-20 would be typical at 75. 16 mpg is low.
My only thought would be to hand calc your MPG. On your next trip, top off the tank until it's full to the fill neck, reset the trip meter, and drive as economically as possible at highway speeds. Run a half tank through if possible for greater accuracy. Fill up to the same level as before, record the gallons to fill from the pump, and divide that into whatever your trip meter mile are. It may be that your mpg readout is off. It should be close. If the hand calc mpg is higher, see your dealer.
If it is the same or close, here are a few things to examine.
1. Alignment. Check for uneven tire wear. You can feel sharp edges on either the leading ot trailing edges of the tread by running your hand across the tread. All edges in the tread pattern should feel the same. If your truck is out of alignment, rolling resistance is increased, tire wear is accelerated, and mpg's suffer.
2. Tire pressure. Make sure tires are inflated to the max recommended pressure listed on the sidewall. Low.pressure can cost you several mpg.
3. Fuel. If you are running a high ethanol blend, you will not achieve the rated mpg. Ethanol has less energy per gallon than pure gas. It may be hard to find pure gas in your state but avoid fuels with higher blends if possible.
Those are the things I'd check. If all of that checks out, I'd definitely document those things and your hand calc test and see the dealer. It is possible that a faulty engine sensor can cause the engine to run rich. I've had MAF and oxygen sensors do this. They can be faulty when new.
Good luck.
