Lean both banks w/ no apparent air leaks

[Fless]

Question , is this a Flex-Fuel engine ?

Not according to the OP's first post.

 

[Foggy]

I'm thinking a weak fuel pump or pump driver module
or, throttle body issue - just my 2 cents

 

[S33k3r]

This is interesting. I have a 2004 Silverado LD; it's running the 6.0, but I'm experiencing the same problem as OP. I haven't performed near the diagnostic or parts cannon work he discusses, but I'm saving my $$$ to take it to a tuner for a more in depth analysis. I haven't hit anyone up for help on mine, yet, as I don't have the time or money to sink into it. But I am close! Frustrating as all get out -- terrible power, and I am getting 10 MPG.

 

[wsteele]

This is interesting. I have a 2004 Silverado LD; it's running the 6.0, but I'm experiencing the same problem as OP. I haven't performed near the diagnostic or parts cannon work he discusses, but I'm saving my $$$ to take it to a tuner for a more in depth analysis. I haven't hit anyone up for help on mine, yet, as I don't have the time or money to sink into it. But I am close! Frustrating as all get out -- terrible power, and I am getting 10 MPG.

Any codes associated with lean condition?

BTW, the OP never came back. Hope he is OK.

 

[Douglas Friedberg]

Wasn’t there something about Pcv valve cover issues with these engines. ??? Bad pcv system will effect all cylinders.