This truck had 450,000 miles when it came into 24 Hour DPF for repair and service. Upon further inspection the After Treatment system appeared to have blockage. Our technician removed the After Treatment Unit, disassembled the unit and upon disassembly it was found to have face plugged diesel oxidation catalyst which caused the truck to lose power and d-rate. After we baked the Diesel Oxidation Catalyst and the Diesel Particulate Filter and the entire After Treatment System. We reinstalled the After Treatment Unit and also performed a idling regen. A complete chassis lube and cleared off all engine codes.