O hmm, that is pretty interesting. I know that Wendler looks low-rep to some people and I know that over time I have stripped it of extra work. Sounds like you have done something similar if you are failing on set 2 of assistance at 50%. I have, at times, lost work capacity, but it has often been a conscious decision to allow for better 1rm growth. At times, I bring more work capacity back into my program, usually 1 set at a time. Maybe you are trapped in a kind of dead end where your PR sets have generally outreached your ability to immediately recover from them, leaving you in this state that you can hardly perform assistance. You could plateau or deload your 5/3/1 for a month while you work back up to 3x8 assistance squats or whatever you think best. Or maybe you don't have enough simple carbs in your system to fuel your assistance after your main lifts. Honestly, I really don't know, but there is surely a simple problem here you can ID and correct. edit: Adding in, the way you are 5/3/1'ing maybe is knocking you out, too. Wendler's suggestion is to keep bar speed strong and maintain good form. If you are doing resting squats to squeeze out a PR plus barely maintaining form and grinding it up, you're taking it further than necessary. Or if you are going for that calculated PR on each and every lift, each and every week, and cheating your deloads, again you are gonna be ground to dust.