good idea, the temp gauge.
and, do you know the coolant mix that's in it, and, how old it is?
Just sayin, if it wants to run hot, you might be well advised to change coolant, use the appropriate mix (usually 50/50), add water pump lubricant (either commercial, or a cup of soluble oil, which I use), add "anti-cavitation" stuff (for diesels specifically, helps for long term), and, maybe even a bottle of "water wetter", for increased cooling capacity.
A general service might be in order.
If, they sold it to you empty, you can't bet they checked things like rear end fluid, trans fluid, engine oil, air cleaner, wheel bearings, U-joints......
Not trying to tell you what to do, or how........and, if you've thought of this all, sorry for repeating.
Just some thoughts.
*edit to echo Elliot re: gas vs diesel*
it's an easy mistake to make......and, can have terrible results.
My army trucks are "multi-fuel" and will actually run on gas, although they really, really don't like it.
But, your 6.2L can self destruct with it.