The 6.0 really needed head studs instead of bolts. There were some anti freeze seepage problems/ head gaskets blowing ect. Many have been converted thru Warranty. Expensive job because the Cab needs to be lifted off the truck. To me the 6.0 drove more like a gas motor which many people like. The 7.3 drove more like a diesel IMHO. I would find the lastest 7.3 .Early 2003 is the last of them. 2001 had a diode in the trans that caused problems but most probably have been fixed by now. The 6.0 does have a much better Trans though , and you should be more worried about Trans issues with the 7.3 than motor problems. I have 2 - 7.3s one with 340,000 and 1 with 297,000. Only thing major was a Turbo and some burned wiring to the injectors/ glow plugs. A DIY job no problem. www.dieselstop.com Best Ford diesel site I have seen.