Aluminum heads...

Years ago was told by a radiator shop that over the course of many miles of coolant flowing through aluminum that the aluminum will erode, the results being a plugged radiator. Any truth?
Reason I ask...my Duramax has developed a small cooling problem. Has a digital temperature gauge. Up to recently the only way to get the temperature above 187* was to put 8000 pounds on the trailer and push it...hard. Like 90mph in 115* heat...climbing a hill. Now, empty, climbing a gentle grade the temp climbs to 200*.