Pulling 8,000# trailer through desert yesterday, temps only in high-80s. Some long, gradual pulls where rpms were 2200, turbo was at 30#. On several (3) occasions I noticed temp heating up - pulled over and let truck cool off before proceeding. This situation seems to come on quickly - not long after temp gets passed the mid-way point where it normally operates, it rises quickly to "overheat" situation. Even with cab heater blowing HOT air, it doesn't seem to help much. Once at my location, unhooking trailer, truck is idling quietly (and within normal operating temp)...then screeches loudly. Similar to a belt slipping or bad power steering pump, only much louder. 6 mos ago, serpentine belt replaced, starter replaced. Oil changed at 5,000 mile intervals. Truck is a 2010 model with 150K miles. Any idea(s) what this could be? Thanks much...I need to keep her running.