Longtime CARS struggler here who made a pretty significant improvement in my score. I literally used everything to improve my score (e.g. AAMC packs, NS108, old EK, new EK, TestingSolutions, and TPR)
I felt that certain aspects of different CARS resources emulated the real deal in unique ways.
For example, I felt that the "passages" from the new EK book were pretty representative of the real test... however their questions and answers were wayyy off.
The passages from the old EK book were not as accurate for the new test (shorter in length it seemed and too easy for readability), although their questions and answers were pretty similar to the actual MCAT. The TPR verbal workbook gave a similar feel to the old EK material... and at times, felt too easy.
Obviously, AAMC material is the most accurate material and I would recommend going through these multiple times if your struggling.
Overall, the best "non-AAMC CARS resource" I found was NS108. The book is fairly cheap, the passages are challenging, and the questions/answers seemed to be the most consistent w/ AAMC material. When I say "most consistent", I felt that their answers required similar logic that the AAMC material did.
Hopefully, this helps... and good luck!