I tried searching already, didn't seem to find an answer.

1xRTT data connection prevent Ring through, and is slow as heck anyhow.

Is there anyway to prevent EVDO data connection with weak signal to drop to 1xRTT data connection? or to prevent 1xRTT data connection all together?

I wouldnt recommend disabling your 1XRTT data (this is possible by doing a registry edit on your ROM). Your SMS and voice rely on your 1XRTT streams. If you notice while you are in an EvDO market and send a text, your indicator will change from "EV" to "1X" while the message is being sent...

Some of the low level features on your phone still rely on 1X data.