ISX cm2350 low. power/poor. Fuel milage.

[JimT]

Also, goign back through the thread I see you mentioned a whistling sound. It's possible you have an exhaust leak somewhere, maybe between the turbo and DPF. This will both reduce DOC/DPF performance AND throw off pressure readings. That could make the ECM think the DPF is less plugged up at the same time it also affects the DOC's conversion efficiency leading to more soot/ash buildup... which the ECM doesn't notice due to the pressure drop from the leak. It becomes a bit of a downward spiral. The exhaust bellows are a notorious place to get a leak and sometimes hard to spot.