2019 Sierra SLT 5.3L 8 speed - I had a shudder as well. Aggressive shifts at very low speed. Like coasting up to a stop sign and then pressing the gas pedal to speed up. Sometimes very aggressive. Took it in and they reprogrammed the transmission shift points (thats what they told me) and it is much better. Not totally gone but about 75% better than before.
I did install the Volant. Performance wise it is very close to the RotoFab. I live in Canada so with exchange the Volant is still pretty pricey. But much less than replacing the bottom part of the air box. The performance is good. The fit and finish is good. The pipe is super smooth on the inside, I was worried it wouldn’t be but it is. I wasn’t too worried about the look. I’m not showing my truck.