A few basic questions- Have you already practiced the GMAT RC so much (and from so many different sources) that you have run out of the material? If no, then what makes you go towards anything else leaving what should be taken care of first?
Moreover, you mentioned that you are 'struggling' with the GMAT RC. What makes you think you won't struggle with GRE RC? And, if you have tried the GRE RC and have'nt struggled, here u are, both of them are not similar!
(Just applying the GMAT CR skills to ur RC query

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