Have you tried driving along with the air-con off,as the compresor could be dragging,also check thermo-switches,is the thermostat opening fully,
. I have a 3.2 and a 3.0 both auto and both have the same cooling systems,ext gearbox coolers,the 3.0 runs at 95 the 3.2 runs at 85 ?
The problem only occurs under very specific conditions : ...
a hot day ... above 20 degrees
caravan on the back
Steep(ish) hill
Kickdown so RPM is held above 3000 rpm
In other words ..
making progress up a hill with the van on the back on a hot day

Given all those conditions the temp will start to rise, quite quickly, and it will go over 100 quite easily. To prevent this all I have to do is to feather the throttle and drop the rpm below 3000, at which point the temp starts to drop quite quickly... but I'm now crawling up the hill at less than 30mph.
This points more at "insufficient cooling" than overheating, and the only thing that has changed in the last 4 years (and it never used to do this) is the fact it is 4 years older and probably 4 years muckier both internally and externally.
Given the other reported problems with miggie rads "silting up" a new rad should sort the problem for another 120,000 miles

Leastways .. thats the theory ...
