Buckleup,
What happened to the 06 RAM you were kicking the tire?
As always when purchasing a used truck you need to do your research to ensure that year doesn't happen to have major problems (i.e. Injector problems or Overheating problems or limp mode problems or worst head gasket problems) which by the way these problems listed are some Duramax problems. :W
I owned a 05 Super Duty and traded it with ~170k miles. Expect to have to pull and clean the EGR valve every 80k miles as a preventative measure. Takes about 30 minutes.
If you do choose to purchase a 6.0 psd powered truck I would look at the 05-07 models. Stick with Motorcraft oil and fuel filters and you've eliminated a lot of potential problems others have experienced by using after market filters in these trucks.
Good luck... :B