I burnt my 3rd. gear band up after going FI, 455 rwhp. It lasted about 2000 miles with about 12 track runs and some aggressive street driving. Would a higher stall tq. convertor help preventing the 3rd. gear bandfrom going;it seems quite few have had the 3rd. gear band go afterbeing FI. The Ford tech said everyting else looked okay. I have since driven about 4000 miles without a problem, however there has been no track time and less aggressive street driving, I did add a deep dish pan.

 

I had the same problem after 3200 miles. My third gear was toast and my converter was unlocking. The stock converter sucks as far as reliability. It can develop strees cracks and they start to unlock on the top end after you throw a lot of power at them. So an aftermarket converter is a gooD idea. I would not waste your time with a TCI converter because those have been failing too. I would probably get a PI triple disc converter.
Replacing the converter will do nothing for the third gear bands. In fact a higher RPM converter will elevate your transmission temperatures because it slips more.
I have a beefed up Level 10 Stage III tranny which has heavy duty bands and clutches. I also went with a Level 10 billett converter.
I would recommend that you upgrade your trans there are a few options out there.You should alsoget a deep pan too. It will add 4 quarts of fluid and help keep temperatures down.
Im pushing over 500 RWHP through mine and it has been fine.