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.