1900rpm at 80mph! Are you serious? if so the gearing is less than ideal or you have oversize tires on it and the speedo hasn't be recalibrated for the tires.
For best milage these motors need to turn about 2000rpm at 70mph give or take, but heavier trucks need more gearing while lighter trucks can get away with less. My 5k extended cab got 13/17 no matter how I drove it with 3.55 gears and 31" tires.. just so you know what is possible.