I need help buying a Cummins.

Hi all, my name is Doug. I'm looking to buy a crew cab Dodge pickup in the near future. I'll have up to $13K to spend, and will be paying $$. It has to be 2WD, and I'd prefer a dually. The age isn't as important as the miles. I really don't want much over 250K on the clock, so I'm probably looking at a '06 or older. I'm not looking for Barrett-Jackson, but I don't want something from Fred Sanford either. I WOULD appreciate any and all help on what to look for, avoid, including what aftermarket parts are worth having. I'm also willing to drive maybe 500 miles for the right truck. Thanks in advance.