Cruising RPM. can it be to low ?

Ex..... you are cruising at 1600 rpms @ 65 mph ...it takes 150 ft/lbs to maintain 65 mph to maintain that speed in your vehicle...but your engine doesnt hit 150 ft/lbs until 1900 rpm.....
Your engine will need more fuel and/or a lower trany gear....so it downshift due to throttle position.... gets back up to 65 and shifts back up into O.D starting the cycle all over again !
Thats my Ram in a nutshell !