Best mods for economy??

[GTP 290]

Hey I was wondering what would be the best options to go for to get the best possible highway economy for my 06 BFII GT-P auto.

Currently I'm struggling to get 500km to a full tank on the highway.

I was thinking of going for a blue power airbox, removal of the rear mufflers for a bit of sound and flow and a re-tune. I was wondering was there any other little bits and pieces that i could put on to get the most out of my car on long trips.

I'm not wanting the greatest results in the world and yes i understand that it IS a V8 but I'm really wanting to do 1 trip in the car without having to stop at every single service station between Mt Isa and townsville.

I would show you a pic of why i am getting bad economy but then this thread would more than likely get locked. The car sits on about 2600rpm in 6th on my long trips.