problem with uploads

I have a problem "uploading" files > 1024 bytes through my router. I
use the term "uploading" loosely to say anything being sent through my
router gets hung and never goes anywhere.

I found several other posts with the same or similar problems and the
answer most of them was that the MTU setting needed to be changed from
1500 to 1492. Most of them reported that this fixed the problem so I
was very excited and thought I had found my answer. Not so lucky, it
didn't fix my problem. I still can't upload anything greater than 1024
bytes via email, HTML forms, FTP, etc. Nothing at all greater than
1024 bytes will leave my router. I can download anything of any size
with no problem. Any Ideas?

Thanks,

Alan