If it has to have a V6 under the hood

[novaderrik]

I may be mistaken, but I think the V6 has cylinder deactivation too

yes, it does... it kills of 2 cylinders, to wind up with a V4- just like the V8 engines... but a little quick math tells me that a 5.3 with 4cylinders deactivated is a smaller engine than the 4.3 V6 with 2 cylinders deactivated. so the V8 should get better mileage when i fuel saving mode, and make more usable power when you need it.
the only time a naturally aspirated V6 makes any sense in a full size truck is in a stripped down short box 2wd that is used mostly for commuting and never really gets loaded down- anything bigger benefits from the extra torque from a bigger motor.