Stang,
That is one pretty bird. I got your PM, but haven't had much time to reflect on it. If you want to pursue doing electrics, the best thing to do right now is to get a wattmeter. If you want to spend some money, skip that but get an eagletree VS with the brushless sensor and the temp sensor. It will really help you figure out what is happening in your power system. I got mine with a $20 of $50 at Tower for about $65, money well spent.

My first impression is that you are either hitting your Low Voltage Cutoff on the ESC, or you are maybe hitting a thermal shutdown on the ESC, but I suspect that would not allow you to restart like the LVC issue. The datalogger would better help you determine what is happening.

We can get you your speed fix, but it may take a little time. Take a look at the other thread here in the beginner's forum about motor/ESC/Battery selection and I reference a program called DriveCalc. It's freeware and it is powerful.
Best Regards,
Curtis