Best Diesel to tow 12,000-13,000 lbs?

Newbie here, so be easy on me eh? My wife & I are just beginning to consider what (used) diesel trucks to consider buying - to pull up to a 13K lb 5'er (not yet purchased). Looking at it another way, what engines and/or drive trains would you advise I stay away from? Diesel is my preference, and 100-150K miles on it isn't a problem if I can review maint. records - oil changes being the most important. We plan to pull the 5'er around 10K miles/year for a few years, out to AZ & back to Michigan. At this point, because there are so many factors involved (rear-end ratios, etc.), I feel somewhat vulnerable in the used truck market. Beyond picking the wrong engine/drivetrain configuration, we're also concerned that we don't wind up with a maint. nightmare or a lemon. Thanx in advance for any & all comments!