I have a ‘21 3500 SRW bighorn megacab and tow a 38’ fifth wheel camper that weighs about 15,500 lbs. I opted with the SO since this is my third Cummins truck with the 68 transmission since 2010. The 68 has been good to me for towing and everyday driving. I tow pretty frequent between the camper, 25’ boat, and farm trailers. I leave the truck bone stock except I’ll put 35” Toyo RT tires on them for added traction. The 68 shifts smoothly when not towing and when towing, there’s a difference when it shifts from 3-4 gear, but that occurs when I just ease into the throttle. It’s not noticeable if you just send it. That’s the characteristic of the 68, it doesn’t mean it’s bad. I’ve driven a 2018 3500 that had the AISIN and it shifted more firmly while not under load. Can’t speak on towing with a AISIN.