X15 2450 low power high fuel consumption

[windowrattler]

You could check for boost leaks, egr differential pressure sensor tubes and exhaust pressure sensor tube. We had a school bus recently that a boost leak and egr diff press sensor tubes was messing with readings. The ecm would slowly keep on opening the egr till it would get to 100%. Fixing the boost leak made it slower to climb to 100% but the mostly clogged egr dps tube cleared out the issue all the way.

For egr from what I know the ecm is after a certain amount of egr flow. It calculates how much flow is happening and if less than it wants it opens the egr valve more. It will open it until it gets to it's commanded flow rate.