My .45 Colt Mark IV, Gold Cup has functioned correctly until just recently when all forms of ammo stopped feeding.
From this statement, we know two things. One is that the pistol was functioning properly as it was delivered, and two is that something changed...and it changed suddenly.
In any feed-related malfunction, the magazine is always the first suspect. Always. Assuming no damage to the magazine, most magazine-based feed malfunctions can be traced to the magazine spring.
Since 800 rounds isn't enough use to weaken the spring, I have two questions.
Have you had the magazine apart for cleaning? Did you install the spring correctly when you reassembled it? An upside-down mag spring will produce the nose-dive misfeed that you describe.