27-37? in one week? That's not too fast. Sure, it's fast, but the pace you are ranking is just slow enough where you are hitting your soft surplus resets throughout the week. There are two soft resets that lower your rank two levels. So, it might seem like you can't get past rank 4 for that reason.

R40-50 in one week is too fast. 27-37 pshhh. Grind harder man.