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.