I have a 06 ISX no def or filter muffler. T-600 kw 07 model truck 501,000 mies 15000 hrs . jsut egr it has been very trouble free compared to the the 2 04 model trucks they where always having egr issues, and wanted to run hot in the summer.  I also have a 01 KW T-600 with a 475 ISX engine  no egr . The avantage to  the 01 is it runs a lot cooler 180 degrees in 100 degree weather on the highway   engine fan  nevers turn on compared to the 07 running about 200 degrees ( 180 degree termoshats new last winter) with the engine fan running about 50% of the time making a horribile roar and taking a lot  of power. Both pulling hoppers . The 01 engine has never had anything done to it with 465,000  miles. The preemmisson engines are worth finding just better and less trouble. Both of my trucks get about the same MPG about 6.5 -7.