What I do know is that my 5.9 litre engine obtains a fuel economy of approximately 21 miles per gallon at 55 miles per hour and less than 15 miles per gallon at 70 miles per hour. Since this is what I drive, I drive accordingly. When I am in a posted 55 I drive 55. When I’m in a posted 65 I drive 60. When in a posted 70 I drive around 60. I’m not in such a hurry as everyone else is I guess.
By the way, my vehicle does not drive at 2200 rpms at 65mph. It’s more like 1800. Maybe you need to recalibrate your gearing or something.
My XJ6 has a 3 speed automatic with no overdrive, and a 2.88 rear end. It’s doing exactly what it was designed to do.
Thing is, you are using your vehicle’s performance as an example of how all other cars behave, and it’s not a valid measure. I bet you have a Dodge truck, don’t you?
Every car has different gearing, that’s why saying “X speed is more fuel efficient” will always have problems. One car might cruise at an RPM sweet spot at that speed but they all won’t. My old 4 speed seemed to have been specifically designed to not do the speed limit, most of the commonly posted speed limits (25, 40 and 55) were all either winding out one gear or bottoming out the gear above terrible for fuel efficiency and unpleasant to drive.