I would use it up and then after 3K dump it and go with Mobil 1 or another oil of your choice. I'm currently running M1 10W-30 SuperSyn in my 02 SS LS1 and i've had no consumption and my motor doesn't have the dreaded LS1 piston slap. Your idea of using M1 and and changing filter at 3k and changing entirely at 6K is what I am doing with mine currently. I would suggest an oil analysis at 3K miles though to see if your M1 can handle the extra 3K miles. Nice Car BTW!