I know a guy with a 1/2 ton Chevy with a 5.3. He pulls a 20' stock trailer with 9 cattle on it. That is probably weighing close to 14,000 lbs. The leaf springs on the rear actually arc downward with the trailer on! He could outpull our neighbor with his 460, and get 10-12 mpg doing it. The 460 got about 6-8 mpg. Our neighbor got a 99 Powerstroke Superduty. The Powerstroke can of course outpull the 5.3, but it gets about 8-10 mpg. I do not know how a 5.4 compares to a 5.3 when being used like this, but I am extremely impressed with the 5.3L.