Mine's been pretty much mothballed, since it can pull about seven MT Heavyweights, and WoT Baggage cars. Not a very impressive Mountaineer.....
I have the decoder in the notch of the boiler, but am intending to move it to the tender. Anxious to see if a few more grams of lead in that notch help anymore, as I've foudn a minute bit of pressure from a finger will increase it's pulling power significantly.
I will note that I tried the scotch tape method multiple times, and saw no improvement to pulling. In on case it made the whole loco worse off, in that the third driver then sat lower then the other three, and could barely make contact with the rails anymore. I don't subscribe to that method as a fix.