Sounds like the orig rcvr had a prob. The rcvr you put in - check the radio, you need to reverse the throttle channel, there's usually a switch on the face of the radio that marked throttle. Flipping that switch will reverse the action so it'll open the throttle when you give it gas like its supposed to.
Remember to always turn the radio on first, then turn the rcvr in the RC on. Then when you're thru, turn the rcvr in the RC off 1st, then turn the radio off.
If you do it the other way, you can have probs and the rc may have a run away.
Welcome to RC Tech btw.....