MPG Motor Magnum vs. Hemi

MPG is calculated the same as with gasoline... Liquid propane tanked versus miles driven.
I've got a phone-app which I use to keep track of the mileage for over a number of years now.
Great (or not) to see mileage rise or (usually) drop based on outside temp differences or (sometimes) changes on the car.

I'm kinda blaming the transmission (A518) and the perhaps in-efficient / old design(?) '60s stall convertor (non-lockup) I've used in it for the crappy mileage the car is getting.