Seemed to be mainly w/ the early production run & maintenance not done properly. Havent come across too many reports w/ 06's that had same issues as 04's.

I had a 06 6.0 as my personnal truck for 2 seasons. under warranty ,dealer serviced and it had issues. and as a dealer we have had 6.0s of all years and they all have issues. they are correctable but expensive. refer to thedieselstop.com/forum
and we no longer will take a 6.0 in on trade or buy at auction unless its cheap or has all the right paper work.
if you buy the 6.0 check your local dealer, ford did offer an extended warranty till 200k thru ford about $1200,if I remember right,its worth the money.your going to use it.

A perfect world would be a late 7.3L PSD with the newer coil spring suspension. My may be converted to such one day.