In my opinion, the A750 is a pretty good transmission. Just gauging by the posts on here, very few issues ever but they do happen time to time. Owning a 4th gen and a 5th gen, I'm satisfied with the transmission but I do prefer the transmission tuning in the 4th gen better. I also own a 2017 Tundra with the AB60/5.7 combo and love it. It's towed a bunch of different things and never has an issue. The common thing with these transmissions is that they feel more commercial/industrial to me than some of the slush boxes in other vehicles, and I'm ok with that.

Regarding the possible 6th gear in the A750, that would be a nice bonus for those that have re-geared really low. For those of us that haven't, I'm not sure it would be worth it since both 4runners barely stay in 5th gear as it is. Maybe that was Toyota's reasoning. The Allison 1000 found in GM HD trucks with the Duramax diesel and the 8.1 gas big block was similar. There was a 6th gear present in the earlier versions but wasn't "available" until the 2005 or 2006 model year. The major differences were the valve body and trans programming.