Odd to see this now, a friend was just searching for a diesel Excursion and going back and forth between the 6.0 and the 7.3. I heard a lot about it. He chose a 7.3.
What I learned is that the 6.0 is good when left alone. Performance boosts may lead to stretched head bolts and then leaks. There can also be some EGR issues.
There's plenty of increase in mileage and power to be had, but when you do it is advisable to replace the head bolts with studs. The studs don't stretch. Kits are available. Then whatever you do in terms of chip or boost, etc. you shouldn't have the head problems.
The work can be expensive, from what I understand it's preferred to remove the body to do the job. Sounds crazy, but that's what they often do. Otherwise it's even more time consuming.
There are videos on Youtube detailing the process.