Diablo is a popular tuner on this forum. If you decide on a Diablo I would purchase it from Moe's Performance, a preferred vendor on this site. He works with Hemifever who will provide a "custom tune" specific for your truck. They usually have some sort of a "package" deal going on, so you might check with Matt at Moe's. A custom tune is far superior to the "canned tunes" that come from the factory with the Diablo. You will also need an unlocked PCM which is part of the package Moe's has. There are other brands of tuners available however I have had no experience with the others and can not speak to how well they perform.
Jay