I think the very best thing for you would be a gear swap. A 5.3 with flattop pistons would be awesome and a dramatic towing upgrade. Stock for stock a 5.3 will be 20% better IMO. The 4.8 is a rev happy motor that isn't the best for towing. The 5.3 also responds much stronger to Bolton's. However, nothing you can do with the exception of a 6.0 swap, is to swap your gears. 4.10s or 4.30s will help you move out quicker and at cruise will hold a lot better. Also reducing stress on the transmission and other drive line parts. A 5.3 with flattops some Bolton's and gears will get you a great setup. Also if you plan to tow a lot you should look at a big trans cooler. My trans temps soar when I tow. Add a 40k true cool and it will stay cool in the hottest summer days.