I actually messed around with it this morning; when in park a/c off I was reading .36-.37 gph. With a/c engaging it would hit .46-.47 gph reading.
While in D I had a base reading of .44-.45 gph and when the compressor engaged it went to .49-.51.

I was expecting the fuel consumption to either stay the same; not decrease when out into drive.

This was on my truck with a scangauge II that was tuned to 5.6%+. Outside temp upper 40's. Both tranny and engine coolant at typical running temps.

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DAILY: 2004 4Runner 4x4 4.0 un-molested, '92 Kawasaki 550 stand-up
PROJECT TRUCK: 2010 DSG 4x4 auto 4.0, 33x12.5, RCD'd, 'Duck-Fart'