New boat not responding

Hello all. I recently took my new Impulse out for the maiden. The first two runs were flawless. About one minute into the third run the boat stopped responding to transmitter inputs. It went straight for about 5 seconds at roughly half throttle then stopped. It still would not respond so I hopped in the recovery boat to retrieve it. As I was heading toward it, it took off again for a few seconds. I finally got it out of the water and it went to about half throttle again and stayed that way until I got it un-taped and turned it off. I checked both batteries and they were still at 70%. I checked all of the connections and they were good. I installed two fully charged batteries and did another range test and all was good. As I went to put it in the water it throttled up and would not respond to the transmitter again. I put it away and we continued running some of our other boats with no problems. Now I have it home and I cannot duplicate the problem. I don't want to just throw parts at it but I do want to have confidence that it will not run off. Any suggestions on how to diagnose this properly. Thanks for any help.