Took my truck on its first road trip today to Flagstaff. 75 mph I got about 18mpg. I'm still surprised. I'm still going to find a 700R4 though as the RPM's we're about 3k-3100. In town the stop and go kills my mileage but on the highway she does good
lol... there's no way. I suggest verifying the accuracy of your speedometer/odometer. Maybe run your cell phone on an app like speedbox where it will log GPS speed and miles traveled for a trip and compare to the vehicle gauges. A 3/4 ton with a 350 and no overdrive is not coming anywhere near that kind of mileage, even on the freeway. That RPM puts you solidly in the range of 3.73 gears with a 30" tall tire or 4.10 gears with 35's. That's exactly what I have on my truck.
It's a 3/4 ton 4x4 with 350/TH400/NP205 and the carb has been dialed in with an AFR gauge. I get better mileage in town due to the lack of OD. I get 10-12MPG around town and 8-10 on the highway. If you had a nice light half ton axle, 700R4, and a well dialed in modern efficient engine, you could be in the 18-20mpg range....
