I don't think killing step 3 would really help you all that much, although doing poorly would definitely hurt. I think your Step 1 and 2 scores will make it really tough for you.
Another barrier is the medicare funding issue.
I think that the government has toughened up on funding people pursuing multiple residencies. My understanding is that hospitals get paid, in part, by the government to have you and use that money to help pay for your malpractice premiums, administrata, your salary, etc. The number of years of funding they get is proportional to the length of the original residency you match into.
For example, if you did 1 year of surgery (funded 5 years) and decided it wasn't for you AND you got lucky and switched into an advanced rads spot (PGY2) then you would have 4 more years of funding to finish your 4 years of radiology training.
Doing IM or FP funds you for 3 years total. So, you are still short 2 years if you switch after your intern year. I don't know how much rads residencies actually need the medicare funding, but they can certainly use it as an excuse to turn you down. If you do Gas you will use up this funding, and it will be that much tougher to secure a rads spot afterwards.
I think if you are REALLY serious about rads you might want to take a year off and do research, if you can find it. In doing this, you don't burn any of your remaining years of funding, and if you make some earth-shattering contribution to radiology, it may offset your step 1 or 2 scores. I think it would be relatively tough to find a paid position to do research, and I think if you aren't doing a residency, any loan deferments you have may be cancelled and you'll have to start paying back your loans which will suck if you aren't getting paid.
A way around the medicare funding hurdle is to talk to the military. I know that 3 years ago the military was offering to fund people for the length of residency in exchange for payback in active duty for an equal number of years. In fact one of my co-residents used to be an FP in one of the armed forces. I am not sure if this program is around any more though.
Unfortunately, I think your step 1 and 2 scores and the medicare funding issue will make it very difficult for you to secure a radiology spot. That is not to say its impossible.
You can try to do radiology research to show your commitment to radiology, and the military may be one option in getting around the funding issue.
Anything is possible-- if you want it bad enough!
Good luck.
-Hans
