Inconsistency a Couple weeks out

I’ve been studying for the last year or so. My diagnostic was 164. A week ago, I logged a 171 and was psyched. But I took another practice test this week and got a 163. I tend to find in my practice sections that I have two modes: either I get a -0 to -3 OR I go like -5. Has anyone encountered this sort of swinging inconsistency? It’s frustrating and I’m not sure how to fix it more consistently. The annoying thing is that in the last two PTs I mentioned above (171 & 163), both of my scores were 178 & 179 respectively. I’m scratching my head and supposed to take the real thing next week. Any advice or encouraging stories would be greatly appreciated! Thanks!