One more note on altitude and cooling systems, and a comment on power output and heat and torque curves. The radiator cap holds a rated pressure differential. Atmospheric pressure drops with altitude. Therefore the ratiator'c contained pressure, and thus the boiling point of the cooling water is lowered at altitude. The 14-15psi rated radiator cap raises the cooolant boiling point by maybe 20-25 degF at sea level. Powering thru sand requires high power outputs. Operating at the torque peak (your 2000rpm range) puts the engine at it's highest efficiency point, and the lowest rate of heat loss as waste to the water jacket. Operating in a lower gear ratio by downshifting or using low range decreases the required engine torque by substituting gear multiplication for engine output, and thus reduces load on the engine cooling system. Low speed vehicle operation decreases the airflow over the radiator, and when accompainied by low engine speed coupled with large throttle opening, the heat input can easily exceed the radiator's heat shedding ability. An electric radiator fan can help at low speeds. I understand that the 2800TDI intercooler is marginal, and is insufficient if the fan does not operate correctly.