The 7.3 is a good engine, the SD trucks have a factory intercooler and a bit more power than the earlier models, but that's nothing that a little money won't fix. The 6.0 is a good engine too, but I would avoid the first year or so of production. The 6.0 also doesn't like big power being added, over 150HP or so according to what I've read. That being said, I've put somewhere between 30-50K on a 04 6.0/torqshift rig, a CC DRW, and it ran really well and never gave the owner any major problems. He still has it, I'd imagine it has around 100K on it now, a large percentage of that loaded and towing. I've pulled 7-10K worth of enclosed trailer up 4-6% grades at 80-90mph all day long with that truck.