sorry for hte delayed reply but I just saw your message. WE usually tow a 5000 # Jeep. My best mpg is about 7 when I keep rpms at 1650. I've tried 1750 and 1800 rpms too. We've changed the muffler to an Aero 5050XL too.
I do almost all my own maintenance and mods so if I can help with anything PM me. Kix