I ran Alco-GE S2's (with Blunt trucks) as well as S4's (with AAR Type A trucks) in yard service at San Bernardino in two yards on 1 % grades, and on outlying road-switcher assignments at Rivera, Fullerton, and Santa Ana.
In the yard, I found the S2's to hold the rail a little bit better when dragging a long string of freshly iced reefers up to the top end of the A-yard. Therefore, I would rate the Blunt truck as mildly superior for tractive effort on yard-quality track. However, the way the engine was run made more difference than the type of truck.
Out on the main line, Santa Fe restricted switch engines to 45 MPH, but (heh) they did not have speed indicators or recording devices. At 45 MPH, even though we had good track, S2's and S4's both were all over the place, slapping from side to side sometimes, and tracking fairly decently at other times. One small horizontal deviation in the track could set them off, but they would calm down after a bit. I can recall a few times when the switching took longer than planned and we had to make a dash for several miles to get in the clear to avoid delaying a passenger train, and I clocked a couple of miles in excess of 60 MPH. The ride quality was the same. They were not designed to be road locomotives, and I am sure that their ride quality was superior to the 2-8-0's they replaced in road-switcher* service.
* For those who live in the East, what we call a road-switcher, you might call a drill.
