MTH RK Challenger Problems on 031

My subject engine 4-6-6-4 runs great over 072 track, but cuts out, stops dead on some 031 curves and Lionel 022 switches. My other large engies (Williams Mike,Lionel 2343 run fine on 031. I have cleaned pick up rollers on Challenger and cleaned track with no improvement. Any thoughts on this RF 4-6-6-4 problem?
Thanks

I’ve got an RK Challenger and it runs fine on O-31 and O22 switches. It even runs fine on O-27!

It did have a problem going THROUGH an new stlye O22 switch.