  We investigate the linear and nonlinear properties of the
Goldreich-Schubert-Fricke (GSF) instability in stellar radiative zones with
arbitrary local (radial and latitudinal) differential rotation. This
instability may lead to turbulence that contributes to redistribution of
angular momentum and chemical composition in stars. In our local Boussinesq
model, we investigate varying the orientation of the shear with respect to the
'effective gravity', which we describe using the angle $\phi$. We first perform
an axisymmetric linear analysis to explore the effects of varying $\phi$ on the
local stability of arbitrary differential rotations. We then explore the
nonlinear hydrodynamical evolution in three dimensions using a modified
shearing box. The model exhibits both the diffusive GSF instability, and a
non-diffusive instability that occurs when the Solberg-H\{o}iland criteria are
violated. We observe the nonlinear development of strong zonal jets ("layering"
in the angular momentum) with a preferred orientation in both cases, which can
considerably enhance turbulent transport. By varying $\phi$ we find the
instability with mixed radial and latitudinal shears transports angular
momentum more efficiently (particularly if adiabatically unstable) than cases
with purely radial shear $(\phi = 0)$. By exploring the dependence on box size,
we find the transport properties of the GSF instability to be largely
insensitive to this, implying we can meaningfully extrapolate our results to
stars. However, there is no preferred length-scale for adiabatic instability,
which therefore exhibits strong box-size dependence. These instabilities may
contribute to the missing angular momentum transport required in red giant and
subgiant stars and drive turbulence in the solar tachocline.
