A novel classical theory of gravity, “gravity shift theory,” assumes absolute flat spacetime and the strong equivalence principle (SEP). Adherence to these postulates necessitates “gravity shifts”—universal fractional length and duration changes—dimensionally perturbing all physical objects and determining gravitational phenomena. Two observer classes emerge. “Natural observers,” using gravity shifted instruments as is, applicable for all presently available observations, perceive a curved “natural metric.” “Absolute observers,” correcting for instrument shifts, measure the absolute flat metric accurately. For a local gravitational system within a negligible-curvature background, the background system’s gravity shifting induces an applied diffeomorphism. Full SEP satisfaction for natural observers is thus ensured—a required critical observational property heretofore predicted by general relativity only. Under the equivalence principle, the natural metric universally couples to matter and nongravitational fields, identifying it as the gravitational metric in physical laws. A unique, parameterless field equation determines gravity shifts and, therefore, the natural metric. The resultant bimetric theory is complete and self-consistent. The field equation yields the observed post-Newtonian natural metric and linearizes to the predictive linearized Einstein equation, which, along with SEP satisfaction, results in successful prediction of a wide variety of observed gravitational phenomena. A supplement is provided that extends the range of prediction verification to include low post-Newtonian order radiation cases, and also the strong-field cases consisting of the properties of black and neutron stars plus nearby matter and light.