A mode shifting apparatus for a decoking tool, a decoking tool and method of operating same. The apparatus includes features to make it rotatably and translationally responsive to changes in pressure of a decoking fluid such that the apparatus is cooperative with the tool and the decoking fluid in a first operating condition to establish a drilling mode with one or more of the tool's drilling nozzles, and in a second operating condition to establish a cutting mode with one or more of the tool's cutting nozzles. In one form, the apparatus includes one or more sets of tandem seals disposed along a component interface within the apparatus or between the apparatus and the tool to help redundantly isolate seizure-sensitive components within the apparatus from the pressurized decoking fluid. In another form, the apparatus includes a gas spring to counteract the forces imposed by the pressurized decoking fluid. In another form, the apparatus includes a manual override connection.