The biggest thing you can do to a 6.0 for reliability is maintain it. Get a monitor so you can see what it's doing. Good good running batteries are critical. A bad battery can wipe out everything from the alternator to injectors. Running a good oil and factory filters are critical to the health of your oil system. Making sure the oil cooler is not clogged will go a long way to preserving the EGR cooler. Once you are sure you have a solid truck you can start saving to bulletproof it with head studs,EGR Delete, updated stand pipes ,dummy plugs,STC fitting......basically making any weak spot the factory missed disappear.
I was afraid of the 6.0 myself and after searching for a Cummins only to realize I couldn't afford a truck that wasn't beat to death I got a 6.0. I have had my fair share of issues but they have been resolved and I can promise you this. Once you drive a good running 6.0 you won't care about the Cummins. If you buy from a dealer spend the extra coin for a warranty. You will have a safety blanket and a road to a solid starting point.