Just completed 4,000 miles...avg of 10mpg

 The HP needed is always lower going slower because the air drag is always lower when the speed goes down. So, when folks talk about a sweet spot what is usually going on is that they have found a speed where the engine is efficient, typically when its running at a low rpm,  just before the tranny kicks into a downshift. Those points are going to vary quite a lot with conditions (headwind vs, tailwind, grade, temperature). There are so many uncontrollable variables that it gets pretty subjective really quickly.

Originally posted by podwerkz It's difficult to convince people of the value of a nearly $200 ScanGauge, but I think they are worth the money for monitoring mpg and transmission temps when towing.  One thing I learned is that, crazy as it sounds, there is a noticeable difference in avg daytime and nighttime mpg...presumably due to the fact that the air is usually calmer, cooler, and more dense in the evenings in my part of the country. Bonus....with the Scangauge (or most other OBD2 readouts) you get air temps, oil temps, coolant temps, avg mpg, instantaneous mpg, current horsepower, exact RPM, error codes, etc.

You also run into the fact that a lot of owners don't care.. 

That too.

Originally posted by podwerkz Instantaneous horsepower and torque readouts are interesting to watch...as well as transmission and catalytic converter temps. Instantaneous MPG readings that vary with road and load, and the avg mpg that is based on each trip since engine start, versus the average over the last several hundred miles (which is common with factory mpg displays). Engine oil temps, coolant temps, torque converter slip ratio, actual intake air temp, etc etc....

I can geek out with the best of them, and I do watch the instantaneous readouts of torque, MPG, etc. However, I find that watching instantaneous things like MPG is sort of like watching a stock on the NYSE; it can make you crazy. I now check these things periodically just to get an overall sense of what I now know to be normal. The instantaneous MPG on our truck has varied a lot; a low of 3-4 MPG if you are going uphill pulling a load to a high of 99 MPG if you're cruising downhill with a tailwind with no load.