You definitely need a tune! What kind of truck are you running? I see 2005 with an LS1 but I doubt you truly have the 5.7L LS1 in it. Do you have the 4.8, 5.3 or 6.0L engine? Are you 2WD or 4WD? What size tires are you currently running? Do you have a G80 limited slip or an open differential in the rear? If you want to be able to launch the truck you're going to need the tune and possibly a 3200+ rpm stall convertor to get that thing to come alive out of the hole.