i would stay away from 01-04.5 duramax trucks. lower on power and torque than the newer ones and had a ton of injector issues. the 04.5+ are great trucks with very few problems.
i've had customers come in before and say they couldn't unlock there car because the keyfob quit working. so awesome to see the dumbfound look on there face when you tell them the key still unlocks the door lol.