I owned Ford diesels for 25 years, going back to the 6.9L. I put 700K between 3 different 7.3L, the 1st being asperated, the last 2 being turbos. My wife drove a F-250 7.3 and an Excursion 7.3 for a combined 190K. Never had a major component failure with any of them and all of them were sold to people or businesses we knew and were in service for many more miles.
In 2007, I needed a new truck. Ford was in a lawsuit with International, based on warranty claims for the infamous 6.0L. They had started building the 2008's with the 6.4 TT, but they couldn't get the engines due to the lawsuit. Any dealer who had some on their lot was not willing to make any deals on them and they were going for almost MSRP. At that time GM, had just had a facelift and they were dealing hard. I ended up with my current C3500 D/A. It now has 170K and has been flawless, minus a 4wd transfer case that was replaced under warranty. I am extremely impressed with the Allison tranny.
My point in all this is, i was a die hard Ford person and had no reason to switch, until the 6.0 L created the circumstances. Now, i have no reason to switch back from the D/A, other than the fact that, deep down, I am still a Ford person. I just feel that their engine/tranny is not yet proven like the D/A. I recently purchased a F-550 for our company, and the jury is still out. It is replacing a 2002 F-450 7.3L that had 302,000 miles towing a 30' gooseneck.