Ya the Diablosport comes with a canned tune in it and compared to the Lew tune it's garbage.
Here's Lew's website -
http://www.diablewtune.com/
You can buy the programer and tune package direct from him and save a few bucks.
He's done enough GM vehicles to know what needs to be done in terms of tune adjustments.
He'll give you a starter tune and you'll drive on it for about 100 miles. Then you'll do a log while driving, send it to Lew and he'll tweak it accordingly. He says it usually takes him 3-4 tweaks. It took him 4 tweaks to get mine dialed.
This is by far the best thing I did to my truck a side from the long tube headers. Those two mods make it an entirely different truck. You got the headers, if you're not happy with it you could benefit from the Lew tune.
I can't see being any happier until the next level of mods, engine work or a blower.
It really did dial the truck in very nicely.
Let us know how it turns out!