First off, thank you for all of the replies.
@dzirkelb: 75 working reps (across ~16 sets) per week never really struck me as particularly high volume. I'll definitely have to think about dropping that to 50ish and doing more dynamic effort + assistance work instead.
@lift206: The pain is entirely on the back/bottom of my glutes. It particularly hurts to foam roll them at the very top, as my ass meets my back. I'm really not sure whether they become less involved as the weight increases, I'll be sure to pay attention next time. But what I do know is my ass is pretty huge, so it definitely isn't a limiting factor strength-wise in any of my compound movements.
@JayPierce: This has to be it. The first 4 years of my lifting were done under the guidance of my high school football strength coach, who valued pushing much more than pulling (we deadlifted under five times a year, squatted every day). I didn't know any better, and have only started actively correcting these muscular imbalances after this past football season, around 8 months ago. My posterior chain is very underdeveloped, so I think that's exactly what happened. What should I do moving forward to help my glutes recover?
@twigs: I don't think I have Piriformis Syndrome because the pain is muscular and I've had no sciatica/nerve pain, but it can't hurt to rule this out.
@lift206: My knees don't typically move inwards when I squat at all but, now that you mention it, this has been happening to a minor degree lately. Another thing I'll watch out for.