I have tried so many things and this engine still runs really slow. Cleaned top to bottom. Tested with another tender. Swapped out the chassis. Swapped out the armature. Swapped out the plastic holder for the armature. Tried different spacers. Tested with and without the smoke unit. The armature still turns slowly when I spin it by hand, like something in the assembly is causing the sluggishness. My only other guess is to now swap fields.