I had similar scores when I started to prepare for GMAT.
GMATPrep : 560, 580, retake : 550 , 620.
Kaplan : 530, 520
Princeton: 520, 570
I would suggest the same as what I did: (It may not be the best solution but it has helped me a lot)
1. Instead of rushing and taking more and more tests. Try to go slowly building solid foundation.
2. Start with Manhattan SC and maintain
error log. (Do SC for at least 4-5 days) Solve as many problems as you can.
After 5 days review your mistakes from
error log and mark the repeated one's with RED (weakness).
3. Powerscore CR bible : try to read each and every details. Solve as many problems as you can after that for 4-5 days.
4. Do the same for Maths: Instead of rushing to difficult questions try to solve simple questions to build foundation.
5. For RC : I need to work on it . So no suggestions. Practice is the key.
After this try to take one test to check your progress.
I repeat: don't just rush to take test.