I finally have had a chance to look at the exhaust and It is not the problem! Seems more a fuel smell than I thought and I can hardly breath in the cab now. I don't see any fuel leaks and it seems to run about the same. It seeems a little sluggish, but not much more than normal.
I took a two hour trip with no load and a fuel/exhaust smell is getting strong inside cab. I cannot pinpoint the exact type of smell, it is not raw fuel or pure exhaust. 160,000 miles on 99 F-350 pwr stroke 7.3. I climbed around and things seem tight, the muffler is getting a little rough...