Have you thought about getting a Tomix chassis and making a powered boxcar/coach to push a Bachmann dummy loco?
Bachmann is not famous for being good pullers. Especially the smaller ones 4-4-0's as illustrated in grymg's post. My Roundhouse locomotives will out perform them any day, as will some of my Model Power, Mikado's, diecast loco's. One of the real challenges with any scale of toy trains is the stoves aka steamers aka valves and so on. If you end up frustrated with them...well...know you aren't alone.
Recheck the tender trucks where the wheels mount to the silver metal axles and check that the tender wheels are not rubbing against the tender frame and each one is free rolling. Also make sure that the traction tires are intact. Each axle on the loco should have a set of traction tires and they should fit nice and tight against the wheels. It is also possible to remove the cab weight section and repack it with Tungsten putty leaving a drive shaft clearance tunnel. Usually the loss of traction is due to the tender wheels not spinning freely.
I don't know how much Spectrum/Bachmann has improved over the last 15 years but I've been really disappointed with the two locos I have for most of the same reasons as others have listed but also because the drivers were poorly machined causing wobble (I guess that is why traction is an issue). Too bad because the locos look really nice. I have a gen 1 Kato Mike and that has always been a solid performer. Back 20 years ago there wasn't a lot of quality american steam (I dislike molded grab irons on the tank) so I started picking up European steam from Fleischmann and Trix and been pleased with their performance but I understand for many running Euro on a north american layout might be considered verboten(LOL). The Kato GS4's are just nice all the way around. I pull their (Kato) 10 car SP daylight passenger set up a 4% grade without issue. The only steam I have I need to get resolved is the FVM Hiawatha. It came as a set with 6 cars but can only pull 3 up the grade. Been happy with my lifelike/Broadway Limited/Intermountain steam. Can't run the AC12 on a full circuit of my current layout though due to overhang on the turns... I need to pull out the chisel and get to modding the landscape.
