Shift RPMs vs MPG. 4x4 AC

I'm curious about the relationship between RPMs, shifting, and MPG. When I first got my truck, I shifted around 2000 as much as possible, thinking that the lower the RPMs the better the MPG. I got around 20-21 MPG (mixed) and a have a camper shell, access cab, and 4x4.

The past several tanks I've been a bit bored, and shift now around 2800-3000. The MPG hasn't really changed at all... most recent tanks of ~75% city driving were all around 20.5. It seems like shift RPM doesn't matter as much as I thought it did.

Is there any explanation for this in terms of the 2TR FE running more efficiently at these RPMs to balance out for working harder?

 

I average 23 mpg shifting my 2.7 at 2,000-2,500 rpms and see no reason to take it over 3,000 rpm. After all, 3,000 rpm is 90 miles an hour in 5th gear on the freeway, which is more than fast enough. My engine has been modded to hit peak torque at 2,900 rpm, so taking it over that is just a waste of gas.


Greg

 

I've noticed a similar trend. The last couple tanks I've shifted typically between 3000 rpm and redline depending on how fast I've wanted to scoot and I'm still hovering just below or above 25 mpg.

Maybe the engine is just efficient at high rpm as well as low. Some engines are just like that. An example of this would be the first gen Honda Insight; it was very efficient when keeping it around 2000 rpm, but that little 1.0L made the most power for the least fuel at 4500 rpm near 90% load, making a 5000 rpm shift point just about the same mpg-wise.