List your MPG on your transplant 5.7 or 6.1

BigBlockMopar said
15mpg with a 6spd (1 overdrive gear?) sounds fairly 'sad' to be honest.
Somewhere in August I made a similar highway roundtrip and managed 20mpg with my propane 318 cruising around 50mph most of the time.

Have you tuned the engine (for economy) properly?

451 bb set on kill, and 80 mph on the interstate. I was hoping for better but that engine is long gone. I'll report back when I get new numbers with a new engine.