Welcome to the forum... 24 is pretty good honestly. The guys getting 27+ have some special circumstances with terrain, and a ton of other variables in their favor.. I only averaged that in mine.
Welcome to the forum! Well it seems you're both lucky and unlucky.. two free engines is lucky, but unlucky you had to deal with it. Perhaps it's a sign to move on? I wouldn't let this motor scare you from diesels... some are just bad lemons sadly.
With tires, you get what you pay for I believe. Even buying a nice mid grade tire is well worth it over some cheap knockoff set. So much is riding on your tires ya know... :D
2-3 MPG overall loss FYI is what I've noticed, even with the EcoDiesel. I don't have a garage currently that I park my truck in so I have a lot of warm up time in the winter, I personally don't care about the fuel lost if I can get in a nice heated cab.