2008 Scion tC, does it get better gas mileage when it's a stick shift?

Yes, manual has better MPG over auto but not that much. The reason is the automatic works by transferring through the torque converter. An ogy is your engine is a fan that is plugged in and turned on. Your torque converter, which drives the rest of the transmission, is another fan (unplugged) that is facing the working fan. The plugged in fan will turn the second fan. A manual is where the two fans are directly linked. Hope this helps.