REALM hit the nail directly on the head. I am trading in my '05 F250, and frankly it has been a good truck. But, too many posts on 'the diesel stop.com' forum about turbos eating themselves and the head gasket lifting/coolant overflow thing.
I came from the 7.3 motor, to the 6.0 and waited until I thought all of the 'bugs' were worked out of the 6.0. But there are still problems being posted on web forums and such. And actually, one of my good freinds, and actually one of the guys who got me into Diesel Power originally, had his 6.0 in the shop (under warranty, thankfully) for the Head gasket/ overheating problem. He is very maintenance minded, and only had exhaust and a drop in air filter added. That is what did it for me. Like REALM, I have been running with a mild tune in my 6.0, and honestly, love driving with it, big torque is a blast! BUT, I keep waiting for the other shoe to drop, and frankly, I don't want to have it drop on my head! OR more to the point, my Wallet.
Like others have said, the benefits of Diesel are being cut into by rising fuel costs, ULSD (instantly knocked .5 mpg off my truck), I don't tow big loads, thus no real need for 650 ft/lbs of torque, 15quart oil changes, Fuel filter changes every other oil change, having to add fuel additives to compensate for the Ultra low sulphur diesel (less lubricity in this new blend, need to add stuff to every fuel fill). When I first got my 7.3 (back in the day) I got 15-17 mph all the time, and 19 if I was careful on the highway, plus the Diesel fuel cost about 20 cents or so less than the cheap gas. Now, the Diesel is as much as premium, or at least as much as the 87, and my fuel mileage on the 6.0l has been as low as 12.5, about 13.5 on average, and my best was just over 17, going 70 on the hwy, for 1 and only 1 trip.
In a nutshell, Toyota dependability. I may put a muffler on this truck, just to hear the nice sound of a throaty V-8, but other than that, she's staying stock, and I am presuming that I'll have a happy ownership experience with my 5.7 DC 4x4.