If you are on a budget, I would go with either the Superchips Flashpaq or the Diablo i2 with custom tuning.
The Superchips makes about 20-22hp/tq to the wheels where we are seeing 30-35hp/tq to the wheels from the Diablo with Hemifever custom tuning. The custom tune is also going to include transmission tuning which will make the truck shift faster/firmer and increase throttle response as well.
Diablo is an overall better option, but the only reason I mentioned Superchips is because it is only $349. The Diablo i2 with custom tuning is $489. The Diablo is worth the added cost IMO, but I understand that everyone is on a budget.