Bullydog is one of the major downloaders. They, like almost all other downloaders, leave traces in the ecm that can be fairly easily detected by a dealer. There have also been some cases where bullydog products at least APPARENTLY screwed up people's ecm's. I don't know the final disposition of these cases, but I do know that at least in some cases, the people received good customer service from bullydog in the form of extreme effort to help them get the problem fixed. Categorically speaking, if you put something other than a downloader on there, the product won't be monkeying around directly in the ecm. That means that such products can't corrupt code in the ecm, and cause embarrassing/expensive trips to the dealer. I don't know if your dad's truck has over 100k on it or not-if it does, then warranty is a moot point.
There is one major thing to keep in mind when it comes to hopping up a common rail cummins diesel (2003 model year and later): Rail pressure. If he ends up putting a box or programmer on it, he should get one that DOES NOT increase rail pressure. There is pretty convincing evidence that increased fuel pressure often damages injectors. One product, the TST powermax, does not increase rail pressure. It makes its power through advancing timing and increased injector pulse duration. Only very recently has the TST released a version of their product that does pressure, and you have to ask for it. The rest of their stuff does not. I think bullydog does.
Before you guys buy anything to electronically add power, I'd recommend you join at least one diesel forum. One of my personal favorites is dieselram.com. Another is cumminsforum.com.
