The test is adaptive except for BEC. If you felt good during the first testlet and then felt like you got your butt kicked in the 2nd that typically means you are doing well. I felt the same way that 1st was decent, 2nd was killer, and 3rd just didn't seem as bad after the 2nd. I take this to be more that I was getting numb to the whole thing.
With AUD I took all but about 10-15 minutes of the time. I've struggled with the written parts in both AUD and REG and I spent an ungodly amount of time on each of my written parts in AUD since I had the time to spare.
On the bright side, AUD seems to be one of the sections that the fewest people have issues with. Based on what you said about the difficulty of the testlets I imagine you did good to great on the MC. If you did well on the MC then an average go at the sims should be enough to push you over the 75 line without too much issue.
I came out of my AUD test feeling ok. I thought I did good but was a bit worried. I felt that I had gotten between a 72-78. Basically I thought I had passed or if not it would be close. I ended up with a 94. This test is horrible for being able to judge your performance. This is probably why most of us obsess over the score releases.
Good luck and grats on being halfway done. I'll be bitting my nails with you at the end of February waiting on the score releases.