  We study the renormalizable group equations (RGEs) of the extended strong and
weak gauge couplings in an ${\rm SU}(8)$ theory, where three-generational SM
fermions are non-trivially embedded. This framework was previously found to
generate the observed SM quark/lepton mass hierarchies and the
Cabibbo-Kobayashi-Maskawa mixing pattern through its maximally breaking
pattern. The field theoretical two-loop RGEs can not achieve the gauge coupling
unification with the minimal setup, unless additional adjoint Higgs fields as
well as the gravity-induced $d=5$ term to the ${\rm SU}(8)$ field strength term
are included.
