2nd Gen Non-Engine/Transmission Hubs Overheating?

[kschitoskey]

I have plastic wheel covers on my dually (came with truck), and on the rear ones I am seeing what looks like heat damage. The damage is on the sides of the center hub cover (next to the actual hub). I have done minimal towing, I run Amsoil in the pumpkin. The rear end is tight, I have not heard any noise (not that I would with the CTD). Is this normal for these plastic covers? How often do these hubs overheat? Don't tell me to get Alcoa's; I would if I could afford them...