Very impressed with gas mileage

I've had /6s that got great mileage, and others that drank gas.
I've had 318s that were the same way. Often in a car "just like the last one I had" but somehow the 2nd rendition was never as good as the 1st.
My dad had a 76 feather duster (early build before 1/1/76, it was a 3 spd instead of the 833OD and still had SBP and 4 wheel drums)
That car and my mom's 79 lebaron "super 6" were the best (of many) /6s for mileage we had.
My 79 d100 wasnt bad for a /6 in a truck.
All the rest were about the same mileage wise as the many 318s we had....