From my experience, the actual questions are easy (as in, you will know how to do them). But factor in fatigue, tiredness, and speed, then they become very challenging.
In terms of study materials, you are fine. DAT Destroyer is really good, and their problems are on par. Then obviously anything else is also good. The problem doesn't come in difficulty, it comes from the things I mentioned above. Honestly, I would brush up on some common questions they give you, and do sets of 40 timed. Obviously if you run out of time, note how many questions you did and continue. After doing a set or 2, you should pretty much cover most of the types of problems they give.
One thing I wish I would have done is stress tests. Doing practice problems in loud places, or play loud music, or after working out. They will help simulate test conditions after 4 hours. Obviously, I would do this after I have a strong grasp on the content. That all depends on your level of math.
All in all, math is like the PAT and RC. It feels hard at the beginning, and then you get better with practice. Just make sure you are constantly doing practice problems. The best tip I got out of SDN was to not stop doing Math a month before the test even though you are killing it, mainly because you become slow again.
Just my 2 cents, hopefully I answered some questions.
