I wanted to pass on how I resolved and issue with my LS in hopes it might help others. I had a weird issue, when I was stopped and I would accelerate, it would accelerate and then sort of die and if you pressed the pedal harder it would carry on accelerating. The engine wouldn't die, it was sort like the throttle was let off for an instant. Also when traveling down the highway with pretty much no throttle, the car would slightly shudder like you were about to run out of gas, or missing on a cylinder. I changed the throttle position sensor and both issues are gone.