lifter or rocker arm?

You can pull the valve covers and check the pushrods, LS1's are notorious pushrod benders, although it's not as common on automatic cars.
If the rockers/pushrods check out, I'd write it off as ls1 tick and be on my way. If you do have a bent pushrod, dont replace with hardened. The next time a valve will bend instead of the pushrod, which is 100x as bad. Go to the stealership and shell out 14 bux for another OEM one.
It may also be an exhaust leak.


