Default An easy way to switch from 3g to 2g mode

I'm on stock rooted Rom and I can't find a way to easily switch from GSM/CDMA to GSM only mode. There are some apps that get you to the networks menu but nothing that would do it automatically. Is there an app that switches to 2g only when connected to Wi-Fi? Please guys, I've been looking all over and can't find an easy way to do that some task.

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