Check the weights.
Have you actually ever had the weights confirmed?
I've come across three aircraft that were way off what the numbers were supposed to be when we actually used the scales. One of them had an actual cog way aft of datum. When I started to tear things apart I found a jackstand base, and two large wrenches that weighed 20 pound apiece, nicely wrapped in bubble wrap tied up in the tail. All in all that plane was 290 pounds empty over the 1675 that it was supposed to be. How long had that extra weight been there? How many flights had been conducted over gross and aft of allowable cog?