Skeeda

I changed my knock sensors 3 times and still getting low frequency code on them. I used Delphi the first time and acdelco the last 2 times. Is there a curtain type, kind or resistance I should be using? I'm at a lost. It's making my 2004 Chevy Tahoe 5.3l Z71 flex fuel run bad and eat up hella gas. Do anyone have an answer? Plz help...