Kaplan might be a good addition, IF you have exhausted UWorld.
And the hard questions of USMLERx to mimic the style of the random Step 1 style questions that they might throw at you.
Kaplan might be better subject wise, because it can test lower yield concepts, and best used after you look at your UWORLD subject percentiles or NBME bars and work on your weak areas.
But UWorld and ALL the NBME self assessments, including the subject-specific ones FTW. Even the newly released Family Medicine ones. There are answers/explanations/discussion forums floating around.