2016 f250 6.7 advice

[MrRobalo]

I’m looking at the truck it’s extremely nice and was a 1 owner fleet truck but was never used as a Truck, even the bed looks like new. My son picked it up at a super price ($20k) from a friend before the auction (he’s a dealer).and he knew we were looking for one. BUT it has 300,000. on the clock. Our thought was to get a F250 to pull our Bullet 220RBI for now but looking into the future a half-ton 5th.Wheel or longer travel trailer. Bucket trips to Blue Ridge next year and following year out west to Nevada. I figure I will get a honest and hands on advice from the forum members that have been going down the road with high mileage vehicles. I know I will have & do (have done) preventive maintenance. One big question is should one always get the transmission serviced ( the best service transmission shop in Orlando) Any advice is welcomed and appreciated.
Thank You in advance