I absolutely love American Flyer. A product that was way ahead of its time.
The slowing down of your trains may actually be the transformer starting to over heat.
I agree with the track comment. The American flyer track has more of a T section which improves pulling power.
My favorite locomotive was the NY&NH 293 and then the 5 digit NYC Hudson.... followed by the little 0-6-0 sloped back switchers.
The smoke units are kind of tricky to rebuild but they keep smoking strong as long as you add fluid.
the red glow from the stack was cool and the chug really takes me back... would really like to find some authentic American Flyer smoke fluid....
And who could forget the caboose with the operating lantern man?
Great stuff. Enjoy running them.