Yeah, my 4.4 is getting about 9.4 l/100 and that's cruising at a steady 125 kmh. I'd ignore the computer and do a test with a full tank run it the refill tank and check the odometer to get another opinon. You're not smelling any gas around the engine or tank are you? Just trying to rule out a possible fuel leak.
'05 GMC Sierra SLT Z71 CCSB 4x4
'00 740i Sport