I recommend billet hold downs and new hardware much more often these days for lly + generations. I have stretched stock bolts, and stripped threads from the head and bent and snapped stock hold downs in a few LLYs. First was my own built truck, and it happened at the end of a truck pull on cylinder 7. Second was a twin turbo stock fuel lly and happened with spirited driving on cylinder 6. Third truck was a workstock vgt truck with 45% injectors and happened several times over a weekend of pulling on multiple cylinders. Fourth truck was my father's, just recently, stock injectors, 425hp tune for 150k miles, 268k miles on the hardware, stretched 4 bolts and bent 2 hold downs - cylinders 1 & 7. All of these trucks ran different tuning from different people and had pretty different power levels.
Just my observations...
Just my observations...