I just got 2 new Dash8-40CWs with the body mt. couplers.
Both of them would not run on code 55 Atlas switches or rerailers.
All the wheels where out of gauge (flange to flange) by .020" to narrow,
causing them to ride up on the sw.frogs & the center on the rerailer.
The wheels side easy on the axles so I moved them out to .301" & they both are running fine now.
Yep, that's what you do when this happens.
So far not a single one of my 13 engines have had any wheels out of gauge.
Luck of the draw I guess. ;D
Now saying that, the next one probably will be out. :o
.301 is "target" according to NMRA S-4.2 (+.002/-.004).
I have found about half of my locos, straight from their respective factories, come slightly tight on gauge. If I don't have problems I leave them that way.
When you have your wheels set to proper gauge, it'll tell on your track work but that's not a bad thing.
It's great that you got them running better.
Good luck