to eyeteeth. just a few ideas from an old technician. Not sure if these are possible on your vehicle, but you can diagnose if its a heat transfer problem or circulation. When you have the vehicle fully warmed up (upper hose is hot), shut off and remove upper hose at radiator. with end held at 45 degree angle, start and idle engine, then goose it to 1500-2000 rpm, there should be a geyser of 3-6 inches come out that hose, if not, your water pump is not pumping. corroded, loose or improper impeller vanes would be my first thoughts.
But before tearing water pump off, check lower hose position and condition as was previously stated. a hose that was not properly trimmed can kink at high temps, and straighten out when cool. or suck shut. laying underneath and revving it up when hot , it should be obvious.
Next heat transfer, if you have the right radiator and you didn't get short changed with a 2 core, when it needs a 3 or 4 row core.
With it hot and running, and if you don't have a condenser in front, you can hose radiator down slowly, spray it lightly to bring down temp then douse it. as it drys out the blocked off rows will stay wet longer. or a HF IF thermometer, but i am old school..50-70 degree temp drop across radiator from inlet to outlet is normal.
also the fan shroud is a requirement, but at highway speeds the ram air should be all that is needed.
air pockets in the block and heads from low coolant is possible, but not likely, but needs to be full, that engine will not hold air in it.
on a lighter note, i read where someone spliced a washer pump into his fresh water supply, and put sprayers in front of his radiator for long hills on his class a 440.
