What engine do you have?
How are you measuring that the engine is using more fuel as you advance throttle, but lose rpm? Fuel consumption should increase with rpm. Have you checked the tps? Many threads here about that. Have all 3 fuel filters been checked? How about spark plugs? What about spark on all 6 plugs? What is your compression on all 6 cylinders? Check it at WOT. Fuel pressure? Is fuel pressure steady as you open the throttle?
What happens when you try to go WOT?
We are trying to figure out if problem is fuel, electric, or mechanical.