As for T.C. being a Captain, remember that, unlike Magnum and Rick, he has been in the reserves since he left active duty. In fact, if he was wearing a jacket, it was probably from his reserve uniform. So he may have received promotions to Captain as a reservist.
Was TC referred to as a Captain in this episode? I don't recall.
However, I do recall that when Magnum flashed back to his Vietnam days when he drove up on TC, Rick and Griff, TC's rank was that of a Warrant Officer, which is common for helicopter pilots. Warrant Officers are not actually commissioned officers, but they are specialists in a given field, such has helicopter pilots.
The only other episodes I remember TC wearing a uniform is "Don't Eat The Snow In Hawaii", "Memories Are Forever", Did You See The Sunrise", "The Look", and "Paradise Blues." It will be interesting to see if TC's rank is consistent from episode to episode.