Hi abused_master,
I don't know if that's your issue, however, when I used the furnace code in GUI, It did not work for me also.
So, I changed my getScaled class to something like this.
private int getCookProgressScaled(int pixels) {
return (this.testFurnace.getField(0) * pixels / this.testFurnace.getField(1));
}
I always use this piece of code for my progress bars, It works like a charm.
Edit: make sure you typed the right values in drawGuiContainerBackgroundLayer.
See if it works,
Alanzote.