Well, welcome to what will likely be the most challenging diesel experience you'll ever have. The 6.0 is like a flirty girlfriend. She isn't going to settle down with you until you give her attention and a ring.
So let's get you started. Before you do anything to it, you need some facts. Has anything been done to it prior to you owning it? Studs? Cooler? Coolant flush/change? Anything?
You need a monitor first. An Edge, or even a cheap OBDII dongle from Amazon, and Torque Pro on your phone. Dial up Coolant temp and oil temp and compare them. Coolant at operating temp should be about 190. If less, the thermostat may be stuck open (common) or a sensor sending a bad signal. At 60mph, cruising, oil temperature should be within 15 degrees of coolant temp and track with it. So approximately 200 to 205 max. This is the delta. Any higher, and the cooler is bad, or headed that way. Oil temp will be higher than coolant temp. Oil cools the turbo, then sheds heat into the cooling system.
How does it start? Quickly? Crank a bit? Romp when cold? Dial up FICM V on the monitor. It should be 48V ALL THE TIME even when cranking. Long crank and romp can indicate a FICM headed south. ficmrepair.com is your friend here. Those guys do GREAT work.
Get those things checked and report back.