I have a 2006 with a 6.0 that was bulletproofed last year. The only issue that I've had since then is an injector that sticks once in awhile. I'm one of those guys who ran a tuner and blew a head gasket.
I have owned Fords for 30 years and have not had any major issues with any of them until the 6.0. I would advice against buying one, though. This engine has numerous design flaws. I've been through two FICMs at over 600 bucks a piece. It has a sticking injector that's going to cost several hundred. The High Pressure Oil Pump system for actuating the injectors is prone to issues and expensive to fix. The variable vane Turbocharger has a history of problems. It cost me over a thousand dollars to have mine cleaned at 100,000 miles.
Bulletproofing also makes it hard to sell them if they had the EGR system bypassed as part of the upgrade. They no longer comply with federal emissions laws.
IMHO - Given a choice, there are better options out there than the 6.0.