Driving with traction control on or off...does it decrease horsepower or gas mileage?

 

depends on how you drive.
normal driving wont even cause the tcs to activate.
turning if off will not increase mileage or power, but will make it easier to smoke tires. (spinning tires still add miles to the odometer)

 

I went on a road trip and tried it off to see if it made a difference. It didn't. I only this week felt it engage so, normal driving wouldn't make a difference.