'kPa' can be seen as an inversed vacuum number.
I could have done the test with a vacuumgauge as well, but the kPa-reading in TunerStudio was more detailed.

100-101 kPa is about barometric pressure = 0 in/hg vacuum = Sealevel airpressure.
50 kPa is about 15 in/hg vacuum
0 kPA is about 29.5 in/hg vacuum

30 kPa = 20.7" vacuum
35 kPa = 19.2" vacuum
So in short, engine vacuum went from 20.7" at idle, to 19.2" with trans in OD.

My MegaSquirt-setup doesn't control fuel yet so I couldn't read any calculated fuel consumption numbers.