Question about a 5.9 in a 2000 Durango

Well, just ready to go on vacation and the water pump goes out in the wifes 5.9 Durango. The thing has 140K on it, so we got our money's worth out of the water pump, it's just that I wanted to change out the timing chain while I was in there, but I didn't have the time. I am going to have to do it when I get some time, but was wondering if the oem timing gears were steel or plastic? I don't know how many miles you can get out of these before they break or wear out, but would like to do it for the peace of mind. Does anyone know what the gears are made out of and if the chain is a roller chain? Thanks for any help.