USMLE Rx was fantastic. I finished it last month. I got the one-year for $199, but I'd say it's worth about $399. Even though you've already hit UWorld and Kaplan, Rx is definitely worth it. Given you're three weeks-out, I would do Rx at ~300 Qs /day x 10 days in timed-mode. At the end of the 8 hours of questions each day, spend four hours going back through Qs and hammering just stuff you saw that day that you weren't 1000% sure about. When you finish the 3000 Qs, dismiss Rx and don't touch it again. Spend the remaining ~10ish days doing FA ~10 hrs/day followed by UWorld again, timed, at 4-5 hrs = 14-5 hr days. I would guess that that would come out to a 5-10 point increase.