The resistivity of germanium containing between N=3×1017 and 1019 antimony atoms per cc was measured at 1.2°K under uniaxial compressions of up to 1010 dyn cm-2. These stresses are high enough to effect an observable saturation in the piezoresistance, that is, to transfer all electrons to a single conduction-band valley ( compression) or to two valleys ( compression). Two distinct ranges are observed in degenerate germanium: for N<1018 cm-3 the mobility increases with N and shows impurity-band effects; for N>1018 cm-3 the mobility decreases and ionized-impurity scattering is the dominant scattering process. The latter range is N>3×1018 cm-3 for large  compression. The resistivity was measured for current flowing parallel and perpendicular to the stress direction. The mobility anisotropy was found to be μ⊥μII=3.9+/-0.1 for N>4×1018 cm-3. This indicates that the mean free path is nearly isotropic. The mobility for electrons in 1, 2, and 4 valleys is compared with Csavinszky's partial-wave treatment of impurity scattering. The change of screening with the number of valleys was taken into account. Csavinszky's theory overestimates the N dependence and the magnitude of the scattering. This is attributed to the failure of the individual-scattering assumption.