I ran two full tanks of HPR during my time in CA. My idle seems to be smooth on the stuff, but a little more lopey.

I got 28mpg on the first which was a mix of hot Highway runs at 75mph (25%) and 55mph country roads (50%) and Fresno/Visalia city roads (25%)

The second was all highway at 70-75mph with ambient temperature consistently around 85F and the air conditioner on for 80% of the drive. This tank netted 29.3 mpg.

Not bad all in all, and with the other benifits, I'd run it full time given the chance. When I switched back to D2 in Yreka, I noticed an increase in engine noise level. I also seemed to have more power, but then I realized that the temperature was 40 degrees cooler. (85 in CA, 45 in OR).

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Garage:

2017 Chevy Colorado Diesel (nanny state emissions)
2005 Volvo S40 T5 AWD, 77k
1987 Mercedes-Benz 300D turbodiesel, 4 sp auto, 156k - 28.7 mpg
1996 Tracker 4x4, 2 door, 16v, 3 sp auto. 113k - 28.6 mpg

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