My computer is running unbelievably slow after installing Avast. Need help.

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I just purchased a new laptop. On my old computer I was using Malwarebytes and Microsoft Security Essentials. On my new laptop, I got Malwarebytes Pro and put Avast. Now my computer is going even slower than my old computer, which I bought six years ago! Downloads, uploads, watching videos, and even just browsing the web is slow. I don't know what to do. I need some help with this. It's too slow for me to be able to use it.

[Pondus]

did your new computer come with a preinstalled AV from factory?
did you remove this, uing that vendors removal tool before installing avast?

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 Running the uninstaller right now and will report back on the speed of my computer as soon as it is finished.