The pen points to the stock 5.7 and 6.1 triple bead valve lock configuration. Stiffer aftermarket valvesprings set up a pinch load on the bottom receiver groove in the valve stem. This can cause separation and a dropped valve. Another flaw is encountered during valve float where uncontrolled movement between the stock valve stem, keepers, and retainer rolls the grooves in the stem. Fred says the problem can range from the creation of nuisance burrs to all out removal of the grooves in the valve stem and is a disaster in the making.