If the operating rr doesn't maintain the wearing points properly, any locomotive truck will ride poorly. For example, the SP's SD-40s (8400s) rode like 6 wheel Pullmans at 70 mph when new, and even when used /and/ the SP took reasonable care of them. By the mid 1990s, however, after several rebuilds (at least once by a contractor), a second or third number series, and the SPs downgraded maintenance practises, they rode so poorly with so much lateral motion that they felt like they were about to derail when operated much over 50 mph. The Amtrak F59s have this problem: lack of adequate maintenance. The CDTX F59s as a whole ride better because they are more carefully maintained.