I used to work as an IELTS examiner and I have found that this is one of the best IELTS exam Trainers:
www.akad.ch/e-lingua
Many private candidates used to ask me about how they could practice and improve their weaknesses. I had to refer them to this as it is diagnositc and supports your development and your weaknesses.
I hope that you can try it out to as diagnostic analysis is imperative for progression in IELTS
