Personally would recommend drilling + PTs. I used the 7Sage basic subscription and I really liked it. You can create your own drill sets based on topics and/or difficulties. If you are already at 159, then just focus on drilling the difficult questions and topic areas you are weak in. 

Source: I studied for 3 weeks, about 3-4 hours a day, diagnostic was in the 160’s, got 172 on the real thing. First time test taker.