Another reason your 336 steam engine pulls all your freight cars is your 336 have pull mor wheels. Like rubber tires. All the other engines you listed do not. The 0-54 curve track you have was made by K-Line. Original Flyer curve is 0-36.
Check some of your local shops to see if they have any good clean used Flyer track. I agree with Mr. Payer regarding the banging noise. Also, make sure the side rods are lubed where they enter the steam chest. As someone else stated, all of your engines need a good cleaning. New brushes and brush springs would help.
Smoke Stack, If I can be any other service, you can call me. My number is 724-479-2026.