I had to play stream maps and play them constantly for two months to get stamina. Every single day pushing my limits, and only then could i do long stream maps with less and less stamina problems. 8 weeks of playing low and medium bpm stream marathon maps. Playing goreshit compilation marathon. Over and over all the time. Nothing but that. Then I could do long streams. I had to take a break for two weeks to let my arms recover from tearing the muscles up so much. Took a week to get back in form, and then I start building yet again, but not as extreme this time. My form has been the same since, and drops back off until I start working on stamina for several days in a row. It is not something that just happens, you have to work really hard for it.