I have a Bachmann Diesel Locomotive that came in a set as a door prize at a model railroad show nearly 10 years ago.  It's not a great model really, but I thought it might be worthwhile trying to improve it...?  I started by trying to find out more about the real unit and that's where things got confusing...

The model is a GP40, (as far as I can tell) painted for the Canadian National road and numbered #5075

Now, from the information I can find online, the real CN unit 5075 was an SD40-2, retired in 1999.

I replaced all the cracked, all four were cracked, axel gears with axel gears from older Atheran engines I've retired and replaced with Atlas, Kato and Proto locomotives. Anyway, after I replaced them, the locomotive lurches like the gears are out of round or don't mess with the tower gears. Am I missing something? I spoke with my local hobby shop owner and he said the older gears would work just fine. The Atheran units ran fine before I removed the gears.
BTW I'm using DCC.
Help please!
John

Does someone know an accurate history of the HO model Rivarossi Allegheny 2-6-6-6??

Where was the original model constructed?

Were there other manufacturers subsequently involved?....not just other owners or distributors such as Hornby and Walthers, but actual manufacturers?

Were any of these built in China, with perhaps different motors etc?