2016 Cascadia dd13 just purchased

I'd start with checking u-joints, steady bearing on the driveshaft and the wheel bearings first.

 

1 and 2 sounds like you bought your money maker without even test drive

 

Your vibration probably could be carrier bearing, U-joints, differential, tires, rims, or loose wheel bearings. First to check would be the driveline for what’s loose or “releasing rust”. Next check your diffs for excessive rotational play.

If you still haven’t found it, I would lift each wheel end and spin it’ll check for a bent rim or mismounted tires. Give them a wiggle up and down to check your wheel bearings.

I would retorque all your wheel bearings at your first opportunity. It’ll extend your wheel seal life and could make your truck drive and feel like a new one.

#2 sounds like the root of all your problems. Sounds like a diff or tranny problem. Could be your vibration and the cause for your ecocruise issue. But I don’t know enough about your autoshift to be much help.

The only advice I’ve got is to dip a finger in the tranny and diff oils and look for shineyvstuff.