[D\/8]

Here's a step by step I posted over on GoodAndEvo:

1. Goto phone dialer and dial *#*#4636#*#*
2. Wait a sec and a sreen will pop-up. Select Phone information.
3. Scroll down to "Set Preffered Network Type".
4. If it is set to "GSM Auto (PRL), change it to "CDMA Auto (PRL).
5. Back out of the page and return to your home screen.
6. Reboot.
7. Repeat steps 1-3 and ensure the changes took. "Set Preffered Network Type" should be "CDMA Auto (PRL).

So far, I have been playing with my EVO for a few hours now, off and on, and the battery hasn't budged... Looking good!!!