My last two tests were 160 (BR 170) and 154 (BR 163). If you look at your analytics, there will be some concepts that you do worse on than others. For your 148, you probably had more of the tougher concepts than the easier, so it's sort of a luck thing once you plateau. It's really frustrating for me, too :/

I wouldn't start drilling before you start core, and even then, don't drill too much until you're done with core. If you go to analytics, you'll see there are different categories of LR and RC questions, and each category will be covered as you move through core. You can drill a little bit while you're moving through core, but I wouldn't start moderately or heavily drilling until you've finished core.

I would continue to study and act like you're going to need to take the January test. If you score poorly, you have 8 weeks atp to improve your skills. I took the September test, scored below my average by 4 points, and then took the November test. After my September test I continued to study, and low and behold I wanted to retake. I'm no expert, but if this is your first test I would study for the next available.

My recommendation is to drill "High Priority" tags only, and drill/BR test sections (35 min) if you are dedicating two hours per study session. Of course, continue to take and BR PTs ESPECIALLY if you struggle with timing.

I wouldn't worry about blind reviewing your first PT just to see how much you've improved in a test-day setting. I would BR for all of the following ones to know which tags you should grind, and also to see if you need to hone in your timing, especially. You could also take them again with unlimited timing. Timing is the most frustrating part for me since I'm scoring mid-150's timed and high 160's untimed, so doing both methods might see what you need to practice the most. I'm not sure where you're at and what your target score is, but I'd try both.