4.8L vs. 5.3L (Stock)
Given the same heads, cam and intake, it is not surprising that the 4.8L produced nearly as much peak power as the larger 5.3L. What the extra displacement offered by the 5.3L gave you was extra torque, through most of the rev range.
Despite the fact that the 4.8L actually produced more power past 5,700 rpm, the additional displacement offered as much as 50 lb-ft lower in the rev range. Even if they make similar horsepower, bigger motors always offer more torque.