May as well add my two-bob. My fuel consumption is pretty terrible. I use between 9.3-9.8l/100km on my regular highway trip (all motorway/highway apart from passing through towns). TJ VR-X auto, 140k kms, regularly serviced, O2 sensor replaced, premium unleaded fuel. My most recent trip was just me, a suitcase and a laptop and I still only averaged 9.5l/100km.

I'm not the most grandpa of drivers (I like to sit at my 5km/h over, thank you very much), but it still seems awfully high.

I've done the trip in my parent's VE SS (06 model, without the feature that shuts down cylinders when not in use) with me driving (same driving style), my family (three other adults) and a bootful of luggage and averaged 10.1l/100km. Yeah it only sits at ~1800rpm on the highway, but it's a V8 and a couple of hundred kilos heavier...