leaning out under normal driving conditions to the point of knock or preignition would make driving very unpleasant kinda like if someone took 2-3 plugs out it would not be happy, also the fuel trims should be trying to keep fuel in line so they would have to be maxed out 20-30% trying to add in fuel before it would reach the limit and then start to lean out, anything like this if its lean using more throttle would make it much worse, if fueling cant keep up with little throttle then adding more throttle just instantly adds more air making the situation worse real quick to the point the engine will feel like its cutting out completely (not good to do) try the 02 sensor if its been a while could help,
02's work on a 0-1v scale 0v being lean and 1v being rich, normal driving when up to temp should see the 02's value shifting above and below the 0.45v constantly thats showing its operating properly, when u go full throttle the reading should be around the 0.80v or above showing its richer, if the full throttle shows under the 0.45 then ur way lean for full throttle