The way I see it, the best year for the 7.3 was 2000. I have a 7.3 in a 99 F 450 box truck pushing 300k miles and it's run great since I got it 200k and several years ago. I read somewhere that in 2001 they went from forged rods in the 7.3 to powdered metal rods. Next, the 6.0 had it's issues in 2003 when it was introduced but by 06 they'd worked out most of the bugs and they were pretty decent. I've also read a 6.0 between 05 an 07 is a hell of an engine and the whole bullet proof thing is mostly needed when you heavily modify and run the piss out of them. The 6.4 and 6.7 have got a lot of haters out there. I don't know much about them.....can't afford one!
Anyway, I'm just starting to build a camper so Ive been researching trucks a lot. I'm thinking a Ford truck with a Cummings from a Dodge and an Allison trans from a Chevy might just be a true dream truck. Of course that's not possible and since I just dropped my wad on a new FWC flatbed Hawk I'm gonna use my 97 OBS F350 that I already own. It's a crew with a 7.3 PSD and 163K on the clock. I'm with you guys though. There's no way an OBS is a worth 20k.... They have a little turbo, small injectors, a Dana 50 up front and drum brakes out back with a weak auto trans and xfer case. Heck, you can find a 2007 6.0 F350 Lariat crew with less than 100k miles for less than 24k...........