Hi Doug,
I say you should have chats with blokes that have gas on still because people I know and including the Tonner I drive (253 Manual) it actually works out Dollar per kilometer gas is about the same,there-for the gas doesn't get used unless it's a long trip or like me take it off the vehicle all together.
If you are looking at the investment$$ and how long to re-coup the saving's my way of thinking it's not worth the effort

Hope fully some one will have a ute like yours and give you the 'good oil'.

Good luck