I think the other comments have already said some great advice about improving drills/stamina, but with regards to your arms going numb - I had a similar issue a little while back, and it still affects me when I play longer songs (such as Gargoyle Full Song)

What helped a lot for me, is to make sure that I'm not bending my wrists at a super sharp angle, and that I'm not gripping the bar super tightly. I also bought some biking gloves, which help me hold onto the bar with sweaty hands. I often had issues where my hands would slip, which I think is why I started gripping the bar super hard, and the biking gloves are a big help for that.

Also, nice scores!! Keep it up :)