You aren't low on oil, correct?
If you lost a head gasket I'm sure you'd see green stuff in the oil by now, or if it managed to stay in the cylinder, you'd never be able to turn it over. No Codes you say? I'm wondering if you didn't loose a cam position sensor, and the ECU is running blind.
Look around online and get the 6.0 bible... there's some pretty good trouble shooting stuff in the back of it. One of the guys here can I'm sure point out the link for the newest revision.
If you lost a head gasket I'm sure you'd see green stuff in the oil by now, or if it managed to stay in the cylinder, you'd never be able to turn it over. No Codes you say? I'm wondering if you didn't loose a cam position sensor, and the ECU is running blind.
Look around online and get the 6.0 bible... there's some pretty good trouble shooting stuff in the back of it. One of the guys here can I'm sure point out the link for the newest revision.