Have you ever loosened all the rocker arms, removed the timing sprocket, and tried turning the cam by hand? When I first got my truck, the cam was practically siezed from someone overtorquing the cam bearing saddles. You should be able to spin it easily by hand if the springs are not being compressed.

When you replaced the timing chain, did you make sure the master links lined up with the dots on the cam and crank sprockets?

A timing chain should last more than 10k miles even if the guides are loose. The chain will usually rub inside of the timing cover for a while before you have an actual failure. It makes a hell of a warning noise - ask me how I know <img src="/forums/images/graemlins/lol.gif" alt="" />