If I may chime in here, as a non-Toy owner - I had my PCM tuned by Black Bear Performance both before and after I had built my snorkel for my Tahoe. (which, by the way, I built mostly for the challenge of seeing if I could make one work for the Tahoe, as noone makes it for me. secondary was the safety in crossing water, etc etc) BBT actually plugs into the computer and goes riding with you, evaluating the engine and adjusting things as needed. At idle, the PCM runs a bit rich breathing the snorkel. But, as speed increases, the airflow crams on into the box and things do change. To quote Justin : it really takes off at 3,000 RPMs. So, I presume there to be a something of an effect from swallowing all that air that is coming in at speed.
So, the snorkel does help a V8 engine.
As an aside- the 'gee wiz aint that cool' reaction to the snorkel has been entertaining. I have had total strangers walk up to me to comment on my rig since I put the snorkel on. Kind of funny.