Ok, the only possible issue w/ the auto would likely be the convertor. However, if its low mileage, and has been well taken care of, and hasnt had a programmer on it, I wouldnt worry to much about it...
Heres a link to whats involved in the heater box removal/repairs:
http://www.turbodieselregister.com/f...-pictures.html
Like I said, the truck may or may not be inflicted with this problem, but its fairly common. Just be sure to check and make sure it DOES defrost the windshield, and does go to the correct position dependant on the position the knob is in. And make sure it blows hot and cold. I dont know how many times people Ive known bought a used vehicle in the summer and never checked the heater; come the first snow fall or temp starts dropping, they finally find out, NO HEATER!!!
Good luck with the potential purchase. Id bet itd be a truck youd be happy with. Ive never had any major problems with either my 03 or 07, minus the self-inflicted auto trans failure in the 07...