Mine had 37k on when I bought it Jan. 2016 Silverado 5.3 with 8 speed. The previous owner had the flush done at 28k. I have 43k on it now. It's been very smooth. I've talked to a lot of people through forums and a few in person who have been very happy with their 8 speeds once the flush was done. And it tows wonderfully, not to mention really good day to day mileage.
There is quirkiness with AFM but I only see it at 45mph and under with a slight vibration. I learned to run in M7 when driving at 45mph or less. No vibration. Locking out AFM eliminates the V4 mode lag. And overall it's even smoother, I no long have wonky downshifts or slams in parking lots.