I second the vote to have an oil sample tested to establish an engine condition baseline. I bought a 1999 about 3 years ago and have been testing every oil change since then. They will help you if you want to extend change intervals. I have been running at 10K mile intervals and the oil analysis has continued to look good. For my use that works out to about twice a year which is good when the change involves so much oil and $.
Good luck with your new to your truck. Take your time and read/listen/learn about it and the 7.3. It's the noisy one but the good one. I have about 225k and it is going strong.
PM if you would like to learn more about the oil sample or anything else on these.
Terry