Thanks drewski11,
But this is just staying bizarre.
First weird thing is how the image is tilted down on one side. I just used a level (with a bubble) and checked the screen. It is level. I even measured, and then checked with a level the top/bottom (Carada Masquerade) screen masks, just in case they weren't level to the screen. But they measured level. I measured the shelf the projector is sitting on. It is perfectly level. I made sure all the feet of the projector are screwed fully in, so it should be level. EVERYTHING would seem to be levelled, and yet the image from the projector is tilted!
Then there's the horizontal lens shift issue. It just doesn't seem to be zooming out equally on the sides. This was the case both using my "pre-centered" lens shift, and then I instead tried shifting the lens shift to get the image centered on my actual screen. It's still zooming out unequally so I have to use horizontal lens shift to adjust the image - just what I didn't want. Not only that I'm SURE during my tests months ago that if I centered the image it zoomed out equally on all sides.
I just don't know what the h#ll is going on. Is it possibly the case that some projector's lens or optics aren't level or something, such that even if the projector is on a level surface the image can still be skewed?
But...all of this may be moot as
my vertical lens shift seems to have stopped working 



. (ETA: Hmm...maybe it's just finicky. Possibly it doesn't work when the image is at the far left of the horizontal image shift position. When I centered the lens it seemed to work again).
I just tried re-centering the lens controls again, this time on my actual screen, shifting the image all the way to the left then all the way to the right, marking those points, then shifting the image so it measures directly between them. This still leaves the image way over to the left side of my screen with my projector lens supposedly centered to the screen. What the h#ll?