Hmmm ... this is interesting. I would like to think that the VG33 engine could withstand 3000 RPM in 4 Lo (especially in the winter), but I'm not sure. 3000 RPM for extended periods of time, with minimal air flow may cause the engine to overheat. I do most of my off roading in 4 Lo; at speeds less than 10 mph (most of the time less than 5 mph). I have never seen the temp gauge climb past the normal mark (not even in the heat of summer), but I almost never rev the engine past 1500.
I would check the coolant level and head back out on the course. Put it in 4 Lo and drive for 30 - 45 minutes; but this time keep the RPMs down around 1500. See what happens. If the gauge starts to climb past the normal reading, take it to the shop for a diagnosis. If there really is a problem, it could be any number of things ... thermostat, mechanical fan clutch, inoperable electric fan, etc.
Maybe 3000 RPMs for 45 minutes of slow speed driving is just too much?
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You've got city hands, Mr Hooper . . . you've been countin' money all your life.