My 6 liter has an annoying habit , at times when I head up a hill as the boost begins to build the truck will momentarily puff out large quantities of black smoke and also at the same instant it will lose power ,not all power by any means but enough that it can be felt through the seat. This is usually a one second duration of so and then back to normal, no smoke and the power returns,then the cycle will repeat itself,at differing intervals depending on load. I recently purchased an edge insight cts and it gives me a trouble code of p404 and then says something about the egr valve not having a full travel range. I took the valve out and cleaned it and this did make it better but it did not eliminate the problem. I am wondering if anyone out there has been through this and if there is a way to tell if the egr valve is bad? I greatly appreciate any help.