[Just1more]

I personally love the allison, but it's pricey to put behind a cummins. As for the the 4L80/85E, I've got a 4l85E behind a duramax in 2006 express 3500 cut away van with a 16' box with over 220,000 miles of heavy work behind it. We used that truck daily to haul barrels and drums of chemicals, often near or over max load for the chassis. Finally retired it to back up status and went to a 2.5 ton chassis truck. I've been more than pleased with how it has held up behind the detuned LBZ, which is rated at 250/460.

However, I think it's all about where the peak torque is and how you intend to use it. The cummins' peak torque and torque curve would be lower in the rpm range, which would definitely be harder on the trans. If you plan to hammer it a lot, I think even a built one would struggle to live, especially if you're fond of nailing it in overdrive.

The 47rh is a bolt on and the cummins guys seems to be able to make them live, so definitely the easiest option in my opinion, but I understand wanting to use a GM trans. I grew up staring at those stickers on the air cleaner that said "Keep your GM vehicle all GM, use only genuine AC Delco parts" and that has stuck with me. It's one of the main reasons I'm having trouble convincing myself to drop a cummins in my dually. I know it'd be easier and cheaper than the duramax/allison swap I'm planning, but I just can't convince myself to do it, LOL.