I had an 04 Duramax, that I blew up.
Chips are safe - to an extent. Good miles on the truck for the year, to start with.
Secondly, depending upon what chip, be careful. 03 didnt have the Allison in it, IIRC
Banks and Edge are very safe chips, they give you codes and allow you to troubleshoot them(at least the Banks does) and both have early warning systems. They also both control more than just the amount of fuel that gets dumped. A cheaper "chip" will just dump fuel, it will increase gas mileage but be careful screwing around
I say go for it, there is an 05 local for 18,300
4" on 35's with a chip, 102k, I wish I woulda bought it