Regarding the OP:
I lump it in there with other misguided generalizations. My favorite one is " my car gets better MPG @70 than at < some slower speed >.
Modern engines are not very sensitive to small changes in RPM. What happens is they get a good tank or two, maybe downwind and downhill
That becomes the new standard and they would rather drive faster than do some real sciencing :P
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2007 Dodge Ram 3500 SRW 4x4 with 6MT
2003 TDI Beetle
2002 TDI Beetle
currently parked - 1996 Dodge 2500 Cummins Turbodiesel
Custom cab, auto, 3.55 gears