My 2003 5.7 has 150k and while I have the motor half apart was curious if I should go ahead and replace the timing chain set. I can get the set for 100. How difficult is it to do?

 

It wouldn't hurt. You basically just need to pull the front cover and harmonic balancer. You will need a new crank bolt as well because it is a one time use torque to yield bolt.
If you haven't already, download the repair manual from weedahoe's sig. Some very good info there.

 

I would be replacing it at 100k. Gotta drop the oil pan to change the chain FYI