I am not a RAM expert but there are a lot of people driving even older diesels, 1990's models for example. Just so long as it has been well maintained, it should be OK. 160,000 miles on a diesel HD truck is nothing. Many have 500,000 miles on them.
I'd get a good diesel mechanic to go over it before you taking a long trip.
With that light weight TT I would not be buying an engine brake unless you personally are having a problem braking on downhill grades. I'm sure you know about downshifting to preserve the brakes when doing so.