73 is a pretty big number too.
I've found, at least for me, that these high rep squats require really really good conditioning. Better conditioning than what I have. As I mentioned, I've done 185 for 40ish, and I've also done 315 for 20. In both cases, leg strength was not the limiting factor. My lungs were on fire, and I felt like I was on the verge of passing out. I would suggest doing as much conditioning work as possible on days you're not squatting to improve this for yourself, if this happens to be your limiting factor as well.