Check or any kinds of molestation. Check for any signs of programers, exhaust, airbags, fifth wheel wholes. When I bought mine I checked over everything to make sure it looked pretty much stock. It had a few things done but was pretty much untouched. I wanted to fix it up how I wanted it. I went from a 2007.5 1500 Sierra sle to a 2007.5 2500 Silverado ltz. I didn't want to go older because I like the newer styling. You should have the 6-speed trans in it. You will have to check the vin to see if it has the LBZ or LLY in that year. Pretty much the same engine in 2006 but has different programming. I would have the injector balance rates tested, check all of your fluids and check for leaks.
It is completely up to you if it is worth it. If you don't mind the styling difference and if you will use the diesel then it is worth it. I got mine because I love diesels, I'm a diesel mechanic so the extra expense that people claim doesn't really effect me. Some parts are more money but just take care of it and it will last you a long time. I also use it to tow my toy hauler and there is no comparisons when it come to towing. If you chose the diesel you wont be sorry. You won't ever want more truck I can tell you that, plus a small tune does wonders on these.
