What I see from the pics ...
You have a 1970's O-scale Lionel locomotive. The power packs are HO scale (smaller) and way under powered for the larger scale loco. But ...
The Railpower 1370 should be able to move the loco and tender around the track at a reasonably constant speed.
First step: (1) Clean the track, the loco's wheels and its pickup rollers (rags & isopropyl alcohol - $2 at the supermarket); and (2) Oil the motor, axles, gears.
Try that. If you still have issues, you'll need to do maintenance on the motor. We can talk you down ...