Check out Amazon or Rock Auto:
https://www.rockauto.com/en/catalog/ram,2016,1500,3.0l+v6+diesel+turbocharged,3353660,engine,oil+filter,5340
Amazon: https://www.amazon.com/dp/B00KQ4VE64/?tag=jhdiesel-20
Welcome to the forum. We have a big thread here about that. https://www.ecodieselram.com/forum/threads/ecodiesel-service-electronic-throttle-control-message.203/
Also a few more. No really 1 thing that causes this is seems. Are you out of warranty?
Welcome! Sounds like you've done a lot of research. If you can score a good deal on a pre-19 EcoDiesel, I would roll with it and give it a try and make sure you like it. You could always trade up in a year or two when the 19' EcoDiesels get a litter cheaper.