I, too, have no idea on the chirping (though more often than not it's been belt-related for m -- just haven't had the issue on this truck, knock on wood).
As for the tune, I'd recommend Black Bear, not because I know anything about Diablo, but because I DO know something about Jason and BB. Jason will walk you through the process, answer any questions you have, and make a custom tune for you. He will suit the tune to YOUR needs. He'll even send you a couple different options of tunes, and you can see which one works best.
And there's no "So, what octane do I have to run?" type of thing to deal with, since you're not getting some "stock" tune. If you tell Justin that you only care about MPG, then he'll tell you what he can do, and then do it. If you tell him you want to push the truck to the point of blowing it up, then he can probably make a tune for that, too (although I doubt he really would). lol
Do you know someone to deal with at Diablo? Maybe you do, but I don't -- but I HAD read a lot about Jason and BB here first, and so I felt comfortable going with them. Well, after I asked Jason a million questions via email first. Then I felt especially comfortable.