  We say a group $G$ has property $R_\infty$ if the number $R(\varphi)$ of
twisted conjugacy classes is infinite for every automorphism $\varphi$ of $G$.
For such groups, the $R_\infty$-nilpotency degree is the least integer $c$ such
that $G/\gamma_{c+1}(G)$ has property $R_\infty$. In this work, we compute the
$R_\infty$-nilpotency degree of all Generalized Solvable Baumslag-Solitar
groups $\Gamma_n$. Moreover, we compute the lower central series of $\Gamma_n$,
write the nilpotent quotients $\Gamma_{n,c}=\Gamma_n/\gamma_{c+1}(\Gamma_n)$ as
semidirect products of finitely generated abelian groups and classify which
integer invertible matrices can be extended to automorphisms of $\Gamma_{n,c}$.
