6.0L cam wakes the 5.3 up. Not really "something little" though, because of the work to change it. If there was much "little" stuff you could do, your van probably would have come that way. Are you hauling around too much crap? Take some out! That's where cheap and easy end. Intakes aren't worth much, exhaust isn't either... Programmers can help some, but not a lot. Axle gears is a good suggestion, but neither small, easy, or cheap.
One of my friends has a 5.3L AWD van that he's using for a HVAC business and he loves it... Says it "halls balls". ?? I wonder what the difference is. (His is a 2010 IIRC)
Good luck!
C