max horsepower
 

Is 425 horsepower too much for stock 6.0 if I use it to get groceries and an occasional drag race?

425 is pretty mild. Just drive it; keep the fluids and battery healthy.

Ok so if 425 is mild, is 475 Ok too? Thing is I'm using the sct sf3 programmer and I don't want to break stuff. Is it OK to use it on performance setting?

Define "use it". As in it's a grocery getter, a daily driven work truck, as a sled puller?

Anything will break if abused routinely. Do you have supporting mods? What's the full picture of what you have done and your driving habits?

Driving habits: I always let the engine warm up before I drive. I usually don't drive more than 15 kilometers until I stop the engine. I don't haul anything. But I often dog it totally at corners. Before i stop the engine i let it idle for a minute ir few.I don't know what you mean with supporting mods but I don't think I have them.

Get the SCT loaded up with some custom tunes. Make sure it's EGR deleted.