Darrell, The core of the radiator was blocked as yours is likely to be. The radiator was removed and recored. A big vehicle radiator shop can handle that pretty cheaply. It was too long ago for me to know the specifics, but it was much less than a new radiator. I have never back flushed or used any flushing materials.

The problem is silicone dropout. I changed coolant every two years and the conditioning filters every six months and used only anti freeze meeting the DD specs, but at 10 years of life the problem occurred.

I think Loc had a similar problem. It is common for an 8V92 to have this problem and it reinforces why coolant maintenance is critical.

BTW, hitting 205 would not have alarmed me, but if it did not stop there then I knew the time had come to address the problem.