Len, You forgot 15.5

eBay, or maybe a Train Show?

That's good stuff Ken!

Litigious liability?
Dunno.
DCC still not for me.

Terry,
No need to buy a new soldering station.
From a Goggle search, what you have is a 15W soldering iron.
That will work just fine for what you stated your intended purpose is, "little bitty wires" and "soldering stuff to PCB boards".
However, that tip will need some attention before you start.

Good luck

This technique works great on Bachmann locos, tenders and rolling stock as well as other manufacturers.

https://www.youtube.com/watch?reload=9&v=6Gf7xqIHGMQ&ab_channel=AthearnModelTrains

Double check all the track section joints to be sure the top of the railhead is level at each.
And also double check the wire connections coming in from the power pack into the speed controller, and the connection at the speed controller going to the track.
There should be no spark. How and where are you creating a spark?

Check the video here;
https://shop.bachmanntrains.com/index.php?main_page=product_info&cPath=265_370_371&products_id=4837

Sounds to me like thermal overload in your power pack from excessive current draw.
Remove the loco shells and disassemble and degrease the chassis and trucks, then re-assemble and re-lube.
Clean track and wheels as Rich stated.

Good luck

https://www.micro-trains.com/index.php?route=information/information&information_id=10

Check wheel gauge.

DC or DCC?
Can you post a photo of your layout? Also showing where the power is going into the layout?
You will need to use a third party photo hosting site.
Bachmann N Scale EZ Track turnouts used to be power routing, not sure they still are.
Can you check continuity with your meter?

Couplers generally fit into a coupler box, either on the body or on the truck. Sometimes there is a screw holding the coupler box in place. On some others a small metal piece serves as the box cover, and holds everything together.

I'm assuming a metal wheel and a metal axle?
If so... use Blue Loctite 242.
Be sure to set the gauge before the Loctite hardens.

You need more vertical easement.
This works for both the top and bottom with or without a turnout at either end.
Easement should be four car lengths, top and bottom for four percent.
Three lengths for three percent. etc. etc.

Good luck

Send it back.
For $300 it should be absolutely perfect.
Settle for nothing less.

Good luck