Not sure if it falls into the same category as your problem - but a while ago I developed a situation where at anything above 2600rpm the temp needle would start rising - and simply keep on going unless rpms dropped back below 2600 again (at which the temp would drop back to normal very quickly).
I flushed the radiator, changed the thermostat and replaced the fan clutch - all to no avail. I then replaced the radiator (new one $280) and the problem was instantly fixed.
IT'LL GO OR IT'LL BLOW!!!