Another observation, if you have ever had any postwar Lionel steam engines, the roller pick ups are much narrower. Most pick up rollers today have a slight bevel on each side of them, but some of them have gotten wider that even what they were during the MPC years and on. I'd be willing to guess one possibility for what is happening, could be that the roller pick up is hitting the ground swivel rail of the switch. Some of my K-Line rolling stock had wider rollers and those could be problematic for me.
But that engine is a 2-8-4, so it's not impossible that one of the flangeless driver wheels is hitting the center rail going through the curve of the switch track.
You might be able to do as I mentioned, and use some electrical tape, or even duct tape to cover part of the top and side of the swivel rail that is closest to the center rail. Or the part where you suspect you are having the trouble.
Might even be the widest portion of the center rail part of the switch track. When I've done that, it doesn't need to be real long, but the tape needs to fold over each side of that center rail. Once you figure out the problem area, I've read where some have used paint to insulate the rails versus tape.
