I reset my MPG average display right before I left the gas station. Got onto the hwy, and set the cruise to 68mph. This was about a 75mi trip. The average was still actually climbing to 21.4, but it was taking it a pretty long time to get there after 20.5 mpg. I just said 21mpg average because it was closer to it. That was with the Nelson tune.
Since I've had it tuned back to stock, the best I can muster out is 19.0-19.5 doing the same thing.
I agree with you about once you enter traffic or exiting into the city, but I was just telling my hwy fuel mileage. I get an average of 16mpg between 40% hwy & 60% city driving.
I don't know about any of you other guys, but ever since they began placing ethanol in the gas, I've noticed an average of .5-1.0 mpg decrease in average fuel mileage. My 01' 3.8L Impala is showing similar results on it's DIC average MPG read out.
Maybe it's just me, but my driving habits have only gotten better not worse.

Jim

 

does anyone else TRY and drive their truck fairly easy and still get 10-12 city and 15-17 highway? im a

 

The sweet spot for rpm isn't exactly related when you don't list a certain mph. Between 52mph and 60mph is going to be the best fuel milage the vehicle is going to get because the transmission will be in overdrive with the converter locked in, wind drag will be fairly low, and the engine rpm should be somewhat low. If you were going for actual highway speeds, the common best rpm is going to be 1800-2000rpm as long as your engine has enough nuts to push you along at that speed with that low of rpm.

 

The best milage comes at the slowest MPH that the trans will keep the converter locked in overdrive.

 

are you positive about that? because what if the comverter will lock up failry low but you can stil go a little faster before you pass the threshold where your engine is spinning faster than the increased MPH is worth?

 

Once it locks, Any increase in speed will be an increase in rpms and therefor an increase in fuel demand. Engines run on fuel, more rpms will need more fuel.

 

True, but the engine load may be higher than you want at really low speeds with verter locked up. The cam specs, mass, and aerodynamics of a vehicle will play a big roll in which RPM and speed is best for optimal fuel mileage when vehicle is in OD.
This is pretty much what Zippy was getting at about your engine having nuts.

Jim

 

lol.....20mpg ill never see that...... i did get 13.5 mpg it was a 220 mile trip and i was hauling a pop-up camper and tryed to keep the speedo at about 63 mph whitch is about 1900 rpm in my truck.. 13.5 mpg is damn good i think in my truck......

 

i understand that but the amount of fuel increae for 55mph to 58mph could possibly NOT outweigh the fact that every hour you are going 3 miles more. just a scenario. i know when you get into higher RPMs the MPH vs fuel usage difference would be outweighed by fuel usage but this may not be the case for a lower MPH to a slightly higher but still relatively low MPH

 

No more than 2000 rpms. Now about speed, that will depend on your gear/tire ratios.