[morepowerjoe]

Not sure you need to rebuild the entire engine but definitely need a top end kit for sure. You didn't day weather it's a ls3 or l99, but I'm going to assume that it is an l99 with the afm (active fuel management) or dod (displacement on demand) where it shuts off the 4 cylinders to conserve fuel mileage and that's where your problem lies. Just in case you don't know there are 8 lifters in there that collapse when it goes to 4-cylinder mode and those lifters fail pretty commonly so, to get the engine more reliable most people just do a cam swap and replace all the lifters with the regular type. Then they go get the afm junk disabled with a tune and depending on what cam you pick you could gain a substantial amount of horsepower. Then you would want to do the upgrades that Vicster recommended. With all the upgrades that I did on mine including parts and labor it came out to around $4500 with a dyno tune. And yeah, that's kind of expensive but I whole heartedly believe you get what you pay for more than ever in this day in age. Like Joshnmn said you can go to Gwatney Performance and build a total package, or I think Texas Speed does it as well. Or better yet just pick up the phone and give them a call and they'll explain everything in detail for you. Hope this helps any questions just ask.