Hi
I have a steam engine MTH 20-3313-1 and it is a 2 to 3 rail type with the same stalling problem.
The locomotive is build with no power pick up and a rear trailling wheel truck with a wiper toutching the axels. The wiper is fixed on an insulated bracket. picture1
The right wheel are not insulated and they are in contact with the right rail (probably the power pick for two rail)
Picture 2 is the two to tree rail tender with the wiper on the front truck
Hope the picture will give you some clue
John