SAT Plateau?

Hey guys, let me give this to you as concisely as possible.

Diagnostic score was 1860, got 1990 in my real SAT. I worked my ass off for a month and got a decent improvement, but my scores just haven’t been going any higher.

I’ve worked through the Blue, Black and Barrons 2400 books. No help.

Can someone recommend what to do in this situation? I wanted 2200 before but don’t think that will be achievable in 2 months, even though I’m prepared to do like 3 hours of work a day.

Thanks x