Select the Letter Cluster that can replace the question mark (?) in the following series. RUUL, WABT, BGIB, GMPJ, ?

LSWT LRXT LSWR LSXR

LSWR

Given RUUL, WABT, BGIB, GMPJ, ? +5 , +6 , +7 , +8 rule is used.  Next term: LSWR G + 5 = L M + 6 = S P + 7 = W J + 8 = R