READ THE INSTRUCTIONS INCLUDED IN THE FILE -- both readme.txt and readme_EC.txt -- (or follow se1000's new guide here) -- you MUST do both the EC flash (WIN4-V08.00.zip) and IC flash (Win4_LCD_Update.exe) to fix the stuttering. The IC flash will not work until you have done the EC flash.
Extract WIN4-V08.00.zip to the root of a USB stick
Boot from that USB stick (press F7 while booting to bring up the boot menu)
Follow the on-screen instructions to update the EC to V08.00
Unplug the USB stick and reboot Windows
Fully close MotionAssistant -- if it is running, it will stop the flash from succeeding.
Run the Win4_LCD_Update.exe as Administrator (REQUIRED -- right click, run as Admin) to update the Display IC
If you have any issues, join the Discord and ask in the GPD Win 4 channel, someone will be happy to assist.