After a search on nonrev.net, I found only one domestic 744 flight on UA which is a DEN roundtrip out of SFO. Flight 770 leaves SFO at 12:50, arrives DEN at 4:14. Flight 595 departs DEN at 5:35 and arrives SFO at 6:58.
It's my understanding that once the 400's come out of heavy MX they cannot be flown overwater immediately. UAL puts them on scheduled domestic ops until they can check the box for overwater ready. This is what I've been told, so take it for what it's worth (not much).
Peak season I have been left behind...along with 50+ of my closest non-rev friends by both the 747 and the 777 between United's various hubs. One Friday p.m. I was standby number 108 behind all revenue and non-rev standbys going DEN-LAX. The DEN-HNL is 777 going and 767 coming this time of year.