Originally Posted by Bilster

As Darth_v8r suggests, if you are going to be pulling trailers, you need to consider low end torque over horsepower....especially if you are factoring in gas mileage. It's not as glamorous building a truck specific motor but you'll get some good satisfaction out of it. Here is what I did to my 5.3. I installed 4.8 pistons to raise the compression (along with honing an already low mileage motor and balancing the rotating assembly). I installed a Comp Cams truck specific cam. I had the 706 heads "truck ported". That is little attention was paid to hogging out the ports for top end breathing and more attention was paid to working the valve pockets and chamber for low lift breathing...where a towing truck mostly lives. Added headers, high flow cats, and exhaust. Then I went with a truck specific tune for the ECM.

Originally Posted by Quick Ranger

The block is the same for 4.8 or 5.3. Crank and rods are different on the 4.8. You could use the 4.8 flat top pistons with the 5.3 crank and rods. Usually it takes compression up to 10:1 or so.