I have been running AmsOil in my 6.4 for over a year. The filters are GREAT!!! no problems at all. I used a AmsOil by pass filter on my last truck. This one got the FS-2500. IF you are going to go for extended drain interval, I suggest doing oil Samples.
IT is VERY important to take care of the oil in the 6.4 even more so than earlier engines. The EGR is VERY high in these trucks.