You are doing better than me. I have been stuck on Quad 3 Back for about 2-3 months, only getting to 4 one time so far. Part of it is the extremely strict settings in the app I am using, which essentially forces you to get like 95-98% accuracy to move forward. The other part is, Quad N Back is too many stimulus to use tricks, so you essentially have to actually improve your working memory to move forward. Working memory is not fast or easy to improve.
There is a guy on YouTube who can do Quad-8-Back, but he is on year 4 of doing it 6-7 days per week. I also think he is using more lenient settings than are on the app I am using, as I do not know if Quad-8-Back is possible on that app with those stringent settings.