Another thing many manufacturer do when testing MPG ratios is that the vehicle is tested on a straight and usually level run or track at about an average speed of 55mph ...no stop and go...no sitting and idling...no slowing down, no speeding up, no climbing up hills or mountain passes, no A/C running, cars...vechicles are "super fine" tuned and tire air pressures set to ambient weather conditions. The cars/trucks are filled with gas in a special one gallon tank remote from the main gas tank then monitored and run until the vehicle runs out of gas. Vechicle fuel gauges are not used just the test monitoring gauges.
There was an expose done on the practice a year or so ago in a program I watched on, if I remember correctly, the Science channel. They never came out and stated the manufacturers but the cars looked to me a mix of then current Fords, Chevy's, Toyotas with the logos blocked out and camo type graphics on the test cars.
It never gained wide spread media attention because who the hell watches the Science channel