As I promised not to bring only bad news...

The problem I referred to in my post above turned out to be the engine temperature sensor (ETS). After reading lots of similar woes by other owners I figured this was the most likely culprit, based on the symptoms. Picked myself up a Power Vision tuner from ThunderTech (in WA) and this confirmed the problem in a matter of seconds. $47 dollars later - all fixed!

Welcome mate and good luck with your issues

 to the forums jme.