Agree with shmoozer^.. These trucks have been around for a long period now and the majority of problems are out here on the web.
When I got my truck the first things were a SCT livewire and a 4inch MBRP turbo back exhaust and a fluids and filters change. If the previous owner said they properly maintained it you cannot go wrong with doing this anyway. I only use motorcraft filters (oil, fuel, and tranny).
You want to monitor what the engine is doing and for the specifications on what all the gauges should be will be right with a google search. Read and make sure you know what to look for. If somethings out of place, you can get a good idea of where from.
1. Monitor/Programmer
2. Exhaust (to lower egts not for sound.. haha yeah right)
3. Blue Spring Mod
4. Egr ******/Oil cooler if needed (if doing the egr might as well)
5. Studs
6. Custom tunes
After this you should know where you want to go with a bigger turbo, injectors, fuel, etc. Most of all, remember to maintain your truck. The 6.0 without proper maintenance can be very costly but if done correctly it will be a very fast and life long truck