^What he said, aero is all the time. Like baseball, you can have an up or down day at the bat, but speed never slumps
Winter is also a crappy time to collect data in general. All my rigs suffer variably with the cold temperatures and wet, sloppy roads. Tough to get a good read sometimes.
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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