This past year we took a trip around the western US transversing 15 states. Temps were high, up to 110 F and several days through mountains pulling a 10,000 pound trailer. The Titan XD perfiormed wonderfully, never had a problem. Water temp, transmission temp, oil temp all remained at normal levels - the exhust temp did rise a lot going up mountains but always returned to normal going downhill. Only complaints I have are that the fuel tank is too small and the filler opening too small to handle "truck" stop fuel nozzels.