Thanks so much for your input, weiwentg.
I attended the accepted students day at university of Pittsburgh and was told they might have some RA position (cover tuition and stipends) available, but it highly depended on NIH grants etc. They do successfully fund the majority of their current phd students (80% or higher). But they cannot guarantee anything before the 415 deadline. Same story with UW, I heard this from the department director.
As for University of Texas, they just told me they had very limited funding source for international students. And Yes, I'm an international student who is not eligible for most federal fellowship or traineeship. Feels like no way to go...