What Bill said x 2 ^^^^
My CRD was OK on sand in WA with summer temps of 35 plus and soft sand etc.
4 x low range and send it, below 2000 it won't even be making decent boost
The 3 litre Patrols have a huge Rad and I reckon either your Fan Clutch is shagged, the lower sections of the Rad are blocked with mud, bug guts etc or the Rad core needs to be rodded (flushes don't do shit).
I doubt changing to thermo fans will make much difference.