The chassis engineering on Sunset locos is often (typically?) not up to Lionel and MTH standards; the modeling may, or may not, be a bit finer, but having to fiddle with this brand a little (or a lot - voice of experience) is frequently SOP. What you are experiencing is not unusual; it has also affected my buying decisions in the past.
When I noticed years ago that my expensive 3rd Rail/Sunset PRR 6-4-4-6 S-1 had no real front truck suspension - even RK locos usually have more - I was mightily un-impressed, and wished that I had waited for the Lionel or MTH version.
