Other news:
The weekend before the trip I went up to the mountains to scout my buddy's wedding location and got to drive this bad boy.
But more alarmingly on my climb up the passes my temps climbed like they had never before. I was running 200 degrees in the block, normal operation even on the passes I never see temps above 190. By the time I got to Frisco I had lost 2 liters of coolant which had puked out of the overflow bottle.
SIDE NOTE: Had I not replaced my instrument cluster with my custom gauges I never would have known that there was a cooling problem until it was too late. Sure the cooling system and engine are 'ok' to run up to 220 degrees or more but I know my rig and could instantly tell there was an issue. These gauges may have saved me from overheating my freshly rebuilt 4.6 1FZ-FE
An inspection turned up no leaks and the belts looked OK so I was terrified that I had a major issue / possible HG. Then the next day I went wheeling with the HJ75 shown above and the temps were all in the green.. I thought that perhaps my fan belts were slipping and / or the radiator cap was failing. A quick call to my buddy's shop and a day later I had OEM parts installed on my rig.
The true test was the following weekends' trip to Moab.
To my chagrin the belts and cap made the difference. I had the throttle wide open from Georgetown (8,530 ft) 13 miles to the Eisenhower Tunnel (11,015 ft), that's a gain of 2,485 ft over 13 miles. The Pict below was taken on the climb about 2 miles from the tunnel, I was shocked to see the engine actually cool down below 180 degrees when the fan clutch engaged.
For those of you who have never been up to the tunnel its a long 6-7% approach, it test cooling systems and truck brakes. Every time I go up it in the summer there are usually 4-5 cars overheated on the side of the road.