  A new time-dependent, scale-independent parameter, \varpi, is employed in a
phenomenological model of the deviation from General Relativity in which the
Newtonian and longitudinal gravitational potentials slip apart on cosmological
scales as dark energy, assumed to be arising from a new theory of gravitation,
appears to dominate the universe. A comparison is presented between \varpi and
other parameterized post-Friedmannian models in the literature. The effect of
\varpi on the cosmic microwave background anisotropy spectrum, the growth of
large scale structure, the galaxy weak-lensing correlation function, and
cross-correlations of cosmic microwave background anisotropy with galaxy
clustering are illustrated. Cosmological models with conventional maximum
likelihood parameters are shown to find agreement with a narrow range of
gravitational slip.
