FTP partial uploads on IIS8

I set up a new FTP server on Windows Server 2012 with IIS 8. When I upload an entire directory, many of the files are cut off and don't match the original file size. I haven't really compared them all but it seems like it might always be 2KB off. If I re-upload that individual file, it will work most of the time.

Here is my log for the latest file that had problems:

21 STOR Quotes.Core.dll 226 0 0 4b2ed740-5b0e-4bb0-8d82-19837385278e /quotes/bin/Quotes.Core.dll
21 PASV – 227 0 0 4b2ed740-5b0e-4bb0-8d82-19837385278e –
52547 DataChannelOpened – – 0 0 4b2ed740-5b0e-4bb0-8d82-19837385278e –
52547 DataChannelClosed – – 2148074264 0 4b2ed740-5b0e-4bb0-8d82-19837385278e –

The file should be 326,656 but ends up 324,800

• This happens to all sorts of files (text, dll, image, config)
• I've set my FTP client (FileZilla) to the transfer types Auto and Binary with identical results
• I've also tried WinSCP
• The server has port 21 open and ports 1024-65535 open for passive in Windows firewall
• I've tried non-SSL and requiring SSL connections with a self-signed cert

I have 2 servers with almost identical configurations and have this problem on both but not any other 3rd party server. Any ideas?