Not to not get things wrong but having D-gas on a 3ltr ,its only a 3ltr fcol,,, I can see a 4.2 needing it
but its an extra fuel ,not for me Im afraid.
Im getting 12 around town and 15 on the hwy towing, which I think are reasonable figures for a 3ltr Auto
Never been a fan of D-gas conversions

Remove it and sell it for what you can