Help me, wifi 5Ghz very slow on Macbook

I read some posts about wifi 5Ghz on macbook slow, but never found any permanent solution.

I am using MacBook Pro (13-inch, 2017, Two Thunderbolt 3 ports) with

Firmware Version: Broadcom BCM43xx 1.0 (7.77.111.1 AirPortDriverBrcmNIC-1710.3)

What I have done, and unfortunately not solving the problem,

• following several articles online about resetting/defaulting the /Library/Prefererences plists.
• and continue to follow the articles, on setting this and that.
• reinstall macbook.
• boradcom driver problem (I actually want to try this, but I don't know how).

After deleting those plist files, and then reboot, the internet become fast around 170mbps (on ookla speedtest), but after sometimes doing works, and I couldn't find out what causing this, the internet seemed slow. So I ran the test again and the result is constantly around 5mpbs.

Please don't say router/internet problems, my android phones and ipad mini 6 easily gotten over 170mbps everytime. But, yes, I even tried several routers, installed openwrt, and obviously wifi settings.

I have not been using this macbook for almost 2 years for work, my daily drivers are ubuntu pcs or windows laptops. But I want to start learning swift again, but frustrated when waiting xcode to be downloaded. Even the android studio, which usually took seconds to download, in this mac takes over half an hour.

Please help me.