Have you performed the basic tasks to eliminate the usual suspects? This includes removing/readding the problem router, PRAM/SMC resets, booting into safe mode, running the WiFi diagnostics (click on icon while holding Option), and resetting Wifi settings on the MacBook Pro? Additionally, is your WiFi router squawking 2.4 or 5 GHz? (if both, which are you using to connect to the MacBook Pro?)