You may have dirty track, inside the tube may be tarnished. Dirty wheels (scrape once/look close). The gunk can look like steel, and be nearly as hard. An intermediate short between ties and center rails? Possibly a smoke unit or other wire shorting too. It may just need the brushes and armature cleaned and dressed. Or the e-unit fingers pressure may be weak/ overheated along the line.
The front truck derailing, clean them. Or pay attention to the pilot truck's guide slot and arch direction.
Do you have other open frame locos that run well?
