On the interstates or other nice highways I put my 2013 D/A on cruise and leave it there unless I have to brake for traffic or a steep curve. Tranny is in D, so it will use the overdrive (6th gear). I run at 65 +/- 3. I usually use T/H until I get up to speed, then disconnect it unless I'm in hilly or mountainous country. I use the exhaust brake in the hills and mountains and (if I remember) when I am exiting the freeway. It really helps keep the speed under control on steep down grades with very little brake use and it helps decellerate on exits as well.
As you can see there are many different practices out there regarding how to use the tranny, T/H, and exhaust brake. I tried many different ways and finally settled on my way as the best I could find (for me) for mileage and comfort. Go ahead and try the different combos until you find one you like.
Safe and happy travels!