When the MMOViper app is running, EVERYTHING lags. My network is completely fine when it's not running, I can game, watch a movie on multiple machines with no lag, but as soon as MMOViper starts, everything gets SOOOOO choppy.

Has anyone else experienced this?

That usually is a sign your antivirus is having issues with viper. You should turn it off while viper is running. Mcafee is the worst, even disabled, mcafee will almost lag out the system.

I run the free version of avast and I have no issues with lag or network lag.

The mmoviper software wouldn't be the cause for your network issue.