That may be a blessing in disguise if its a 4.8l! If it is a 4.8is it could be the valve stem seals and more. This seems to be a common problem and a very expensive fix. I have heard stories of $5000 with no gaurentee it will fix the problem. The valve guides wear and seals will not do it. in this case new heads are incolved costing upwards of $10K!
Now the 4.8 is a totally different animal than the 4.4's and the 3.0's. They usually have some type of CCV/crank case vent issue. Could be the CCV valves, plugged CCV hoses, plugged ports in the valve covers or many other simple fix issues.
I'm going through this right now in my 4.8is hoping for an inexpensive cure. Just joined this forun tonight trying to see what info is out there.