interesting observation there, I understand the fear
The conditions you describe are normal driving. Any speed, for any amount of time of normalish highway driving shouldn't overheat your oil. That being said, it would be good to see what the temp actually is. Easiest way I can think of is to use a temp gun on the filter/lines feeding the filter up on the fender. It is possible the smoke you are seeing is water evaporating out of the oil, or smoke from blowby becoming entwined in the oil. If there are puffs of air coming out of your oil fill, it is prob the latter.
IMO oil temp is something people get skittish about too easily, at least when dealing with synthetic oils (which I gotta recommend for turbo things). Oil needs to get hot to stay clean, like 220F as the lowest operating temp. The teen years of the corvettes sorta opened my eyes to this, with their oil temps being considered good up to like 310F. Sounds extreme, (cause it is) but it helps proves to me that oil works just fine at temps like that for a while. Another thing I think i know is that oil is going to always be 20-30 degrees hotter than your coolant, so take that into consideration. If you decide to change out your tstat, be sure to look into the effects of that on the trucks computer. I cant remember for sure, but I believe the truck still believes it is warming up at those temps, and might run less good than it would hot (without tuning)
To add an oil cooler means you are adding fittings, hose and a cooler which all become potential (catastrophic) failure points. I do not recommend unless you can prove a significant need. General highway travel does not warrant such a risk.