Silverado Engine Choices

I am asking advice for a friend that is usenet impaired. He is considering buying a Chevy Silverado pickup (2 wheel drive). His only heavy hauling would be a 5,500 lb. trailer from Minnesota to Arizona once a year. Both the 4.8 and the 5.3 V8's are rated for 7,500 lb. The 5.3 comes with a 3.73 rear end and the 4.8 a 4.1. Would the higher rear end ratio with the 4.8 negate the (theoretically) better mileage of the 5.3? Any opinions about the relative virtues (or bad points) of these two engines would be appreciated. Thanks.