GM has the WORST emissions vehicles on the road; and, as a group, the worst fuel economy. In fact, they're worse now than they were 5 years ago, don't believe all that MPG crap they're bombarding you with in their ads. Ford has the best emissions and, believe it or not, the best overall fuel economy for domestic vehicles
Not as far as trucks are concerned.The most common engine on the 1/2 tontrucks where I live are the 5.3 gm and the 5.4 ford.The 5.3definitely gets better mileage than the 5.4.I have owned two gms and two fords and the gms average about 10% better mileage.This also agrees with the fuel mileage charts given out by Natural Resources Canada.