Before everyone heads off to Goroka, you had better have your rig tuned up. To get to the PNG highlands, one drives up the Markham valley until you reach a mountainous wall, you drive up the Kasam pass (Yobar read up on it) this road deemed an impossible engineering feat by the engineers in WW2, starts at about 120 feet above sea level and you reach the top at about 5000 feet. This is one climb, in which on the way up you drive through the clouds :), there are amazing views to be seen, but don't come off the road because you wont stop rolling for hundreds of feet.
My Landcruiser came with two sets of carburetor jets, one set for sea level and one for the highlands.