I don't run out of upgrade instruments ... but that's because most of my UA travel is between SFO and IAD, with travel dates usually determined about a week in advance. Even as a 1K, my upgrades clear less than 25% of the time on that route.

The last few trips, I routed my outbound through San Diego. I don't mind getting to my hotel a little later in the evening than compared to a non-stop if I can get an upgrade, and so far, upgrades have been 100%. In fact, on one flight on a 757, a third of F was empty, including the seat next to me. Fares have also been cheaper routing that way.