Inferno,
On page 776 of this thread Grizz posted a link. Go to that link and click on tech tips. In that tuning guide it says exactly whats wrong if you have a lean bog at 1/2 tank I just checked it to confirm thats where I saw it. It's in bold print about half way down the page after you click on tech tips on the left side. You actually need to richen the HSN 1/2 an hour at a time according to them as long as your Idle and LSN are set correct to begin with. You really need to go and read that guide! It's linked on the first post of page 776 on this thread!