I have kept thinking on this, because I know it is troubling and frustrating for you. Me too, really. 18 years and I've only had 1 chick die in all that time. I think we need to go back to the basics:
What kind of bedding are you using? (Cedar is not good)
How often is bedding changed/cleaned? (that many chicks means a LOT of cleaning)
What kind of feed are you giving them? (Chick starter is recommended, no treats until later.)
Any additives to water or feed when they arrive? (Nothing, unless you have a very specific problem.)
What temperature in the brooder box, and do you have a thermometer in there at chick level? (90-95F the first week, decrease by 5 degrees each week)
Can the chicks get away from or closer to the heat lamp? (Smothering shouldn't be a problem, unless they are too hot or too cold. They should not be piling up.)
Do you have multiple feeders and waterers? (For so many chicks you need LOTS of both)
Is any food getting wet? (moldy food is deadly)
How often is it replenished? (Food should NEVER run out, nor should water)
Any drafts from windows, doors, central heat or air? (Close vents, prevent drafts. But fresh air is a necessity)
How much space overall for how many chicks? (Chicks need a lot of space)
I'm not being mean, I'm trying to help because I suspect you have a basic problem and we can solve it.