Rohn007,
Thank you again for your replying!
Yes, it is still under Dell warranty, but since Dell wanted me to try remote service first, I sent the laptop to the Dell Depot, but received it back without no improvement. Recently, Dell checked the issue and said they would send me a new one, but actually
they sent me a refurbished one and the same issue is seen.. That's why I hopelessly started posting online question for the first time.
Again thanks so much for taking your time to answer. I appreciated it!
=====Update 05.23.2016=====
I just wanted to leave some follow-up comments regarding this issue.
Dell finally offered me system replacement few months ago, so I received a brand new system. That means I had tried three Dell XPS 13 models: 1)
the original package I initially purchased, 2) the refurbished system, and 3) the
brand new system Dell offered as a replacement.
I found all of them had the same issues I mentioned above, which made me wonder whether the issue comes from the compatibility between Windows 10 and high resolution screen in general. Then I wondered why technicians I had talked to were not aware of these
issues if this was merely due to high resolution screen. I would have not wasted 6-7 months of time for something that wouldn't be fixed by system replacement...
Anyway, after realizing that even the new replacement had the same issue, I didn't try further to solve it. Hope future updates from Windows, drivers, or XPS models would solve them one by one.
Rohn007, I have very much appreciated your support to try help me out though! Although issues still persist, I learned a lot through the discussion.