The other thing that makes a difference is the final drive ratio. Some autos have a taller OD gear, and with modern converter lockup they have an advantage on pure highway tests at speeds above practical P&G speeds. Can't really take advantage of coasting at Mach 2 in a brick.
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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