Given the competitiveness of fellowships these days, any little thing that makes you less desirable to a program will decrease your chances at getting an interview and getting accepted. If a program has 100 applicants and 99 of them have already taken their step 3 then the first one to get thrown aside is the one not having taken step 3. It's not so much that programs are concerned with your performance on step 3. They just want to know you've taken and passed it so that you can get licensed and wont end up forfeiting your spot in the event you can't pass it. Step 3 is a bs test. Take it in your intern year when step 2 material is fresh on your mind and put it behind you. Like the previous post said you'll want to be able to focus on residency and your in training exams and not on bs med school stuff you'll never use again. God luck.
