[kathyricks]

For about $40 any smog shop will test your HC and CO emissions at idle and at 2500 RPM. Ideally, HC readings should be in the single digits ( 1 - 9 ppm) and the carbon monoxide reading barely detectable. But if HC readings are around 50 ppm or higher then your engine is burning excess gasoline or one or more of your emission system components is degraded.

Or you can simply start spending money on normal tune up items for a 95,000 mile Toyota that could improve fuel economy: spark plugs, pre-cat oxygen sensor, air filter, manually scrub throttle plate clean. Look at the old spark plugs. One or more spark plugs should look blackish if the engine has been burning an excessive amount of gas.

Is there even the slightest chance you havn't been calculating the fuel MPG correctly?
The usual procedure is to fill the tank until the "first automatic click" of the pump shuts down the pump. Then drive about 300 miles and refill the tank again until the "first click." If the tank took 12 gallons to refill then 300 miles divided by 12 galllon = 25 miles per gallon.