I have 2003 non HO. Did injectors at about 220,000 miles. Upgraded to FASS pump and filters at that time because I don't want to buy injectors again. Keep an eye on the trans temp. I added a deep trans pan as well. If you don't have gauges, then get some or an Edge or something that lets you see what's happening. Nothing wrong with watching your EGT either. The dash will crack if it isn't already. There is an airbag recall and some have a front end recall.

The late 2003 HO cummins has more power, so that would be a plus. Its easy to make these engines make a lot of power, but then you start breaking stuff, starting with the trans. And the "bulletproof" trans is $$ unless you built it yourself. Its been a good truck and I've got about 270,000 miles on it now.