HO all day for towing in the mountains. I live in the mountains in Colorado and the Aisin is fantastic out here. Add the torque of the HO Cummins and that exhaust break and it's a killer combination. When I was looking at used trucks a while back every 3500 so I saw with more than 80k miles had had the trans replaced. I think they have heat trouble towing heavy in the mountains. Imo there's no downside other than price to an HO.