What to look for on this truck, need help...

Ok, just bought it.........

I did a search, but couldn't find the info right off.

I'm going to look at a 2003 2500HD D/A after work. It has 144K miles, crew cab, royal blue, tan leather, LT with quite a few options. Appears to have some drivers seat tears, and some door dings. Also a few small dent/dings behing the rear drivers side wheel. Wife looked at it and said it looked nice beside that. Said it smelled heavily of smoke, but I can get rid of that. It has a paint matched ARE topper on it too. They are asking $15990 for it, but think I could chat them down. My worries are the miles. Should I worry? I know they are suppose to last 300K miles. I also know that the injectors are waranted for 200K miles. What should I look for? What should I ask. This will be my first diesel experiance. I'm a quite capable gas man, but not so steady on the diesel. Any help would be great. Thanks,

Mav