Just returned from my first road trip with a brand new RAM 1500 Limited Longhorn with the standard 3.6L V6 gas engine, 3.21 ratio. Estimate total load of around 600 pounds included self, wife, bikes, normal road trip stuff (not towing anything). The truck had less than 500 miles when we set out from the California Bay area to the San Juan Islands in Washington State, with stops at points in between.
Total Distance: 2,293 miles
Average MPG (actual): 18.4 MPG
Average MPG (reported by RAM trip computer): 18.3 MPG
Average speed: 46 MPH.
Typical highway cruising speed: 60 – 75 MPH
MPG varied from 16.8 to 20.6 per fill up. No clear trend. Variation probably caused by going up/down Mt. Rainier, Mt. Hood, variation in speed, etc. as well as percentage of ethanol (0 to 10%).
Overall, considering the comfort and utility of the truck, I am very satisfied with the mileage. Sure, it is worse than my wife's Prius, but try driving that on a 2,000+ mile roadtrip and maintaining good humor the entire time. Plus I would have probably left the bikes at home, and that makes the trip so much more fun!