You need to provide more inputs to enable us to suggest some concrete strategy.
Here are my observations
1. Firstly, it's not a good idea to compare your performance or measure your improvement by comparing your score on the Kaplan tests with the GMATPREP tests. If you go through the forums, you'll see that the algorithm on the Kaplan tests is not very reliable .
2. Did you analyze the GMATPREP test you took lately ? And if yes, what are your specific observations about your performance ? In which areas did you struggle on the Verbal section or on the Quant section.
3. You may be a victim of the "I got 80% accuracy" syndrome which eternal_optimist mentions in his post (Here's the link
https://www.beatthegmat.com/3-yrs-4-atte ... 72531.html )
This is one syndrome which a lot of us suffer from . Ask yourself that how good are you conceptually ? How well can you apply the concepts learnt ? How strong are your strategies ?
Your query is quite generic and you may want to be as specific as possible in order to trace down the root cause of your lower- than -expected performance.

Cool, yeah that is really useful stuff, thanks! I am going to take a course to try and help be get better as the books alone are clearly not doing it for me!