When people talk about tone... it can be tricky... because it's all about what sounds good to the individual... What sounds "muddy" to you... may not be "muddy" to me or the next person... But the way I interpret "muddy" is that it sounds bassy, distorted... without a lot of characteristic in the high and mid range.... Try cutting your Bass waaay back... like down in the 3 or 4 range... your mids in the 5-6 range and crank your treble way up. That may not get you the tone you're looking for... But that should give you a good starting point for dialing in an Iommi sound...