"stressly go down ""smooth"

I just tried that and I do hear a tone difference. We don't normally listen for tonal differences as much as you would. I know I've heard Spanish speakers saying can't and having it sound like a stressed can. It takes practice to hear a language that is as different from your native language as English is from Chinese. All I can say is keep working on it and good luck.

And keep coming back here and your English will improve as you practice.

Also, aside from some linguistic terms used by professional linguists, I don't think we really have the language to describe the differences in stress that you noticed and referred to as "stressly go down" and "smooth".