A big thanks for the great support. 
Connecting the “nRESET and nSLEEP” to GPIO 3.3V pin did the trick. I have been able to set Vref to 675mV and it is very stable.
As for the heat sink, I agree with you it is not really needed, I am going to use the heat sink and a small fan (30mm) just to ensure the chip is nicely cool and happy. I also know the chip can be hot enough to burn your fingers but the chip is fine and working perfectly.
I also plan to use a TL Smoother just attempt to smooth the motor steps.
Agan thanks for the info and support.