My Buick is burning gas fast, I just got a tune.

Use a gage and check fuel pressure, not only check for correct pressure, see if pressure will hold for a bit, with everything off. If pressure drops like a rock, you got something leaking. If the fuel pressure regulator has a vacuum line, take the line loose and see if fuel in the line, if so pressure regulator is faulty. You could have leaking fuel injector?

If your evap system has a leak, you can smell gas. Any applicable trouble codes? Smell of the engine oil dip-stick, does it smell like gas?