How to upload a large file with more than 500 mb to a ftp server using asp.net application

I changed the web config from 4 mb to : 2,147,483,647 bytes and also increase the httpsession timeout
dev server it works fine and uploads up to 800 mb without an issue. But on the stage server, it doesn't support even 400 mb file, I get the error: Bad gateway or Gateway timeout error
Is the issue from IIS Server in stage?
Is there any other solution is there for this issue because the dev environment the c# the code works fine but same source code(c#) on the stage server does not work.
Kindly help me out from the issue
Thanks,
SASIDHAR C