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I have an 01 LS1 with a TSP 233/239 cam, roller rockers and lifters. Lately driving on the highway has introduced a valve tap on the drivers side, usually after cruising at highway speeds for a decent amount of time. Of course when I first heard it I started to think it was a valve adjustment issue...but it goes away after I let it idle for a minute. It has been come and go, usually only appearing on the highway. Now I'm starting to think it could be a lifter is going, but they are relatively new. The pushrods were swapped to the correct sizes when the cam and lifters were installed. Ideas? I'm trying to see if I need a day to adjust the valves, or a weekend to pull the heads. Thanks guys.