My stock JLUR will not hold 6th unless I am doing 75+. That gets the engine spinning just fast enough for cruise to hold speed. With sport gears, I would just leave it in 5th myself.
I sort of suspected that the the really high top geared MT was probably a fleet MPG strategy and so that you say the same for ATs in that it rarely goes to 8th gear appears to support this hunch. The fact that the MT requires drivers to shift whereas the AT, which is supposed to be very good (I wouldn't know since I own a MT), does it all behind the scenes without driver having to think about anything is probably the simple reason why we hear so much about it from MT and not AT owners. Right? I haven't heard any AT owners complain that their Jeep doesn't use 8th gear or can't maintain 8th gear at 65mph, or has to shift down to 5th gear when passing or going up hills. Most AT owners don't need to know or want to know what the transmission is doing.I can only speak for the 3.6 gas version, but it doesn't hold 8th much, even stock Rubis running 4:10 as standard. The moment you drop bigger tires on it without regearing, the only time you'll see 8th is on a downhill with a tailwind. That said, you don't really notice it on the 8 speed, because it's so damn slick at the gear changing. It really is a remarkably well engineered transmission, and is well matched to the new generation of 3.6 Pentastar.
As someone else already mentioned: these vehicles are geared for theoretical emissions standards. And we all know the EPA numbers are BS anyway, but the manufacturers need to make the numbers work.