Agree here - check wood chip type - make sure they are pine, not cedar. What type of chicks are you hatching?
So sorry you are experiencing this!
Sadly, the primary reason chicks die in the brooder is dehydration. I know you're at the "I've tried everything and am seriously at my wits end" point, but give yourself some time to step back and evaluate everything, and more than likely the solution will come to you. We've all had catastrophic failures when incubating and brooding chicks, and somewhere between "I'm quitting the chicken business altogether" and "Can I just learn something not the hard way???!!!" a solution usually presents itself. Reevaluate your process, read some good brooding articles, have a glass of wine (or beverage of your choice , and start again tomorrow.