  Measuring the magnetoresistance (MR) of ultraclean {\it GaAs} two-dimensional
holes in a large $r_s$ range of 20-50, two striking behaviors in relation to
the spin-orbit coupling (SOC) emerge in response to strong electron-electron
interaction. First, in exact correspondence to the zero-field
metal-to-insulator transition (MIT), the sign of the MR switches from being
positive in the metallic regime to being negative in the insulating regime when
the carrier density crosses the critical density $p_c$ of MIT ($r_s\sim 39$).
Second, as the SOC-driven correction $\Delta\rho$ to the MR decreases with
reducing carrier density (or the in-plane wave vector), it exhibits an upturn
in the close proximity just above $p_c$ where $r_s$ is beyond 30, indicating a
substantially enhanced SOC effect. This peculiar behavior echoes with a trend
of delocalization long suspected for the SOC-interaction interplay. Meanwhile,
for $p<p_c$ or $r_s>40$, in contrast to the common belief that a magnet field
enhances Wigner crystallization, the negative MR is likely linked to enhanced
interaction.
