replaced everything....

1974Duster, replaced all parts of the front end. New uc arms, new ball joints, all tie rods and sleeves. all bushings, idler arm. didn't replace pitman arm or gear box. Duster steers great for a while and than alignment goes to crap. any suggestions? New torsion bars, and spc upper control arms. almost everything that could be replaced was. ty for the help.