How is it going?
Pumping can cause injury. Especially if the pump is malfunctioning in any way, or mom is needing to pump very frequently and/ for long sessions. So the pain you reported worried me.
Pumping can pull fluid into the areola which can cause issues as well. Basically, the physiology of pumping is different than nursing, so issues can crop up.
What about adding hand expression to your routine? Hand expression will not cause the same issues as pumping, also, that may be a way to help with letdown. Breast compressions while pumping may help as well.

You are pumping 40 ounces a day? That is a lot! How much is your baby drinking?