Overheating in NW Mountains

That was going to be my suggestion, but you beat me to the draw.

 

You're not that bad. One can only improve by wanting to be better, and you are doing precisely that by asking questions.

 

Yep

 

The copper bulb on a thermostat if full of a type of wax that expands when heated.
If a small amount that of wax leaks out of the bulb the thermostat will open at a higher
temperature and wont open all the way causing the engine to run hotter. Thermostats are not expensive to replace.
If the belt is squealing it is slipping because its worn out and can be contributing to your problem. Replace the belt and while it is off manually spin all the tensioners and idlers the water pump and alternator and A/C pump. If anything sounds even a little rough or has excessive play replace it. If an idler or tensioner pulley comes off it can do a tremendous amount of damage.
Like a couple previous posters said make sure the coolers in front of the rad and the
rad are clean.

 

That sounds like air to air leaking .. does it smoke black if so that contributes to excess heat also.

 

Yeah that sounds a little more like a boost leak to me.

 

Start with that as does your truck not have a belt driven water pump?
Once worked on an N14 that would run hot loaded up hill. Several others had thrown parts at it. The belt condition and tension seemed acceptable. Connected a pressure gauge to the coolant passage at the RR of block. Do not recall what it read on the road but probably about 35 PSI. When the engine was do shifted, RPM's increased and a faint belt squeal started. At that exact time the coolant pressure would drop. The temperature would rising shortly afterwards. Simply tightening the belt stopped it from over heating.
Along with things others trash can get packed in between the coolers and be able to be seen until they are separated. That is condensor, radiator and charge air cooler.