If you're going over the river and through the woods to Grandma's house for Thanksgiving this week, you'll be paying a little bit more at the gas pumps.  AAA-Michigan says the average gas prices across the state have risen six cents a gallon this week.  The current statewide average is just over $3.53 per gallon, which is nearly 20-cents more than the Thanksgiving holiday a year ago.  The auto club says the price spike this week can be blamed mostly on increased demand for the driving holiday weekend ahead.  Monday saw local drivers seeing pumps asking about $3.56 a gallon for regular unleaded.