To add to that,
The standard Omega 3 fan set up, with it's original relays, thermoswitches and wiring is more than good enough to keep a supercharged LS1 cold, so there's not much you can do to cook a 3.2 Omega without seriously abusing and neglecting it
I'm para about overheating, Actually it's never stranded me, but I've had a few times I've had to drive with heating on full pelt on a hot day, just to get where I'm going.
How? By driving everywhere at WOT? In Second? Towing a trailer? With the hand brake on?
My 3.2 didn't overheat once in 180,000 miles, even sat idling for hours at a time in full summer sun. The 3.2 cooling system is identical to the 2.6.
What did I miss
ECU and gauge temperature sensors.
Gearbox oil and filter change.
Not replacing the thermoswitches whilst the radiator was out.
Testing the fans to ensure that they're working correctly.
Replace the header cap (and bottle if it's excessively discoloured... increased likelihood of age cracking around the neck and therefore evaporation leaks).
Always keep the aircon on. If you see ECO on the climate display, slap yourself, press the ECO button once and slap yourself again. ECO not only switches off the clutch on the compressor, it also turns off the front fans unless the coolant gets really hot.
Put that another way, as long as the aircon is on , both front fans will run at full speed, the rear fan still switches according to coolant temp.
Make sure the brakes aren't binding, especially the hand brake. Check it, adjust it, re check it.
Driving lessons. It shouldn't be getting that hot if you drive it normally. A 2.6 isn't a 3.2 so stop driving it like it is.*
*This is slightly tongue in cheek, but if you're regularly in the exceeding the upper mark on the temp gauge, then you are either abusing the car or there is something wrong with it/gauge sensor is faulty, making the gauge over read.