I've had the 2018 dually about 2 weeks. Traded the 2016 SRW in on it. Both with the Aisin so I have no way to compare. I've got about 1,000 miles on the new one trying to break it in before I load the Bigfoot. When I hit 600 miles I hooked on the 5th and towed about 150 miles. I got the Torklifts on last week. My plan is to load the Bigfoot and go trout fishing next week.
To Aisin or not to Aisin, that is the question. For me I have trouble saying no to more horsepower and torque. I don't remember what the Aisin allows the Cummins to be tuned up to in comparison to the 68, it's not a lot, but it was enough to snare me.
The maintenance will be higher for the Aisin. They call for a drain and replace at 30,000 miles. It's just drain the pan so only 7 quarts. I let the dealer do it just for having a record in case of later warranty issues. My little small town dealer said they don't ever recall doing that. At 60,000 it's drop the pan and a new filter.
I have the BigWig off the SRW in the garage waiting to get installed on the DRW. Not sure if I want to make a trip without it just to see how the DRW does or go ahead and put it on now.
Not much help for your decision but that's all I know.
add: My payload went from 4018# on the SRW to 5406# on the DRW. Both spec'ed the same, even the color.