We have 2 06 6.0's an 03 6.6 and an 08 6.7 and by far the 2 6 leakers have given us way more fits, one is studded with tuned FICM, 155cc sticks by Ryan caserly, and a billet turbo by Adrian, the other has bullet proof EGR cooler straight pipe both have SCT and blue springs and lift pumps, also both are flogged HARD on a daily basis, and both go down for some bs reason about every month or so,
We have resorted to changing oil about 500miles before required... And running rotella synthetic tripleP
I would try to talk him out of it if u can, if not check the oil cooler and engine oil temps for the cooler, EGR delete it, flush and run CAT ELC coolant in er, EGR delete, and make sure the fuel pressure stays above 60 psi or u gonna be buying injectors.. : ( blue spring help keep the pressures up, and upgrading the drain tube on te HPOP will also help, belong an later 6.0 try and see if it has the newer larger oil drain on te charger they are less likely to clog...
But get ready to maintain that pig!
I will say when they are running right they are STRONG trucks, it's just keeping them up that's a PITA!