My wifes daily driver is a 2001 Tahoe with the 5.3. At start up when cold, a knock is heard. My dealer is telling me that it is because of the shortened piston skirt, and the roller lifters. Other vehicles do it in varying degrees of noise. The noise disappears on full warm up, the oil psi is great, no smoke or oil consumption, and great power. Do any of you have any experience or advise?