Are the tail pipes sooty? I have read that they should be clean and if they show signs of soot the DPF is most likely cracked.

If it smells like coolant it could be a leaking egr cooler or head gaskets. I am not too familiar with the 6.4, but thats what happens when the egr cooler goes in a 6.0

Could a moderator move this to the 6.4 section so it gets more exposure and the op gets the help he needs?

Sarge