So I've been noticing some lifter noise from my daily driver lately. It's very repeatable, it doesn't do it in stop and go traffic or city driving, but if I drive on the highway with a sustained rpm of 2000 I will hear it after only a few minutes of driving. 2003 GMC Sierra with a modified 6L. I see no change in oil pressure, temp is good no lose of power I just can't hunt it down and want to be sure before tearing the heads off the truck. Could it be possible for a lifter to be collapsing even at a higher rpm?