It is a fairly long story of how I ended up to this point but I will try to filter as much unnecessary information as possible.
I ended up with a '97 F250 with 92,000 miles that had been setting for 4 years. Apparently the clutch had exploded and broke the transmission housing. So when I got the truck it needed a clutch and transmission housing. That wasn't a problem to fix and much to my amazement the truck started on a couple cranks. No funny noises on the first start just lots of white smoke. I was not to surprised about the smoke due to the time it had been sitting I figured the injectors were probably dry.
It turned out to be pretty dogish up to about 2,500rpm and then it would come alive and run just fine. I drove it a 1,000miles on a one way road trip and at over 75mph or about 2,500rpm it would run fine. I was only getting 10mpg or so but it ran. When the problem didn't clear up I started investigating and found the back to cylinders on the passenger side were running cold, and when I unplugged the injectors the only change was no smoke. It also had excessive blow-by that could be seen by taking off the oil fill cap.
My tried swapping the injectors from the front to the back but the problem didn't follow. So the next thing I did was pull the head.... When all the rocker arms were pulled it was apparent that the two exhaust valves on the problem cylinders were higher then the rest, giving the first sign of the real problem. After I pulled the head it was pretty clear that each cylinder had dropped the exhaust valve seat. The damage can be seen in the pictures.
All the symptoms add up perfectly to this but I would have never guessed that the valve seats would have failed.
The reason for posting this is to ask has anyone ever seen this problem on a power stroke? I did some searching on my own and couldn't find anyone with the same issue. I would be more likely to think it was a random seat problem if I didn't have 2 side by side. My guess would be that heat played a major role?
Link to Pictures
Head(Look at the valve height)
Cylinders (Notice the pieces of the seat)