Interesting test.

Is the kPa that TunerStudio calculates something similar to
“Brake Mean Effective Pressure” BMEP?

With the Oztrip meter one readout is gallons per hour consumption.
When my Magnum 5.9V8 is in warmed-up idle using gasoline without ethanol the Oztrip displays 0.65 GPH.
If I turn the high beam headlights on at idle this will rise to 0.66 or 0.67
If I turn the air conditioning on at idle this rises to 0.71