L'any 1944, la Pacific Railroad va construir la número 6131, que va reorganitzar les lleves i cilindres, solucionant el problema de la Q-1, creant una doble lleva 4-4-6-4.
In 1944, the Pacific Railroad built number 6131, which rearranged the drivers and cylinders, solving the problem of the Q-1, creating a duplex-drive four-four-six-four.