There should be plenty of GPU successes next week, as around the 4th July loads to and from the USA are generally low.
I had to change a flight, and the [already applied & confirmed] GPU cleared at booking:
1. PEK-EWR
2. July 3
3. W
4. Y-J
5. changed 2 weeks before departure
6. Cleared at time of change (asked agent to look for days where flight would clear at booking, and not be waitlisted)