Haven't flown UA in a while but wow - upgrades are impossible. I am 1K and I have two upcoming flights.
1. 1K on G fare #10 out of 22 on the upgrade list. 20 F seats, 3 seats open, no checked upgrades.
2. 1K on T fare #27 out of 60 on the upgrade list. 48 F seats, F is full, no checked upgrades.
No wonder I am flying AA as EXP and many times #1 on the list - and clearing.
At least on UA - I will preboard before group 1, if they announce it. Last time on UA, they announced Group 1 after they did GS.
There will be lots of preboarders on my flights.