Yeah having done this exam last year in January, i agree it is tough, though Uni is definitely tougher, so think of this exam maybe as a preparation and bridge between University and A level exams. Exam technique is crucial for an exam like this where an understanding of the principles is needed to be applied!
Past papers will go a long way, I found I learnt a lot more from doing the past papers from 2002 - 2008, and looking not only at the mark scheme but the examiners reports. This exam can be done and is doable and if you are getting 66% + on raw marks you are probably about A grade standard.
If they didn't have a module like this where there is so much content it would not be able to stretch the most able physicts, tbh so be happy that there is a module which is challenging!