5/3/1 is not for powerlifting. That being said, here is your problem:
Your warm-up is nuts. Let's say your true 1rm is 285lbs. 90% of that is about 255(rounding down a pound). You are doing 5 attempts above 90% and that is after going to failure on, essentially, a 5rm. This has nothing to do with work capacity or your nervous system, it is just not a good plan. Your warm-up should be just that, a warm-up.
If you goal is to find out where your max is at, you only have one work set... the last one. Nothing else should be too stressful. I max out twice a week, every week, year round and this is the basic warm-up I use (not saying this is the end-all be-all most perfect strategy but, it works and I don't feel like shit 95% of the time).
Warm-up- Max Upper Body
Shoulder Mobility work for 5-10mins
Bar for 2-3 sets of 10-20
Slow jumps in weight up to 50% of my previous max then:
60%x3 or 5 depedning on how I feel
70%x1 or 3 depending on how I feel
90% or 92%x1 depending on how I feel
95% or 97%x1
This way, the actual warm-up isn't killing you and you are only going over 90% 3 times at most. Especially doing 5/3/1, you don't have to worry about things like your nervous system. You already recognize you do more sets/work or whatever than other people... maybe that isn't a good thing.