change it, but send a sample off to blackstone labs or similar for analysis. I'll bet it will come back saying it had many miles left in it. But it will give you a baseline and some real data on how often to change.
I too was a every 3,000 mile change guy. But gradually after doing oil analysis at increasing miles am very comfortable with the roughtly 10K mile change the on board computer says in my duramax and the 7500 mile change interval for my cars. In both cases even at 10K miles, TBN (total base number) which shows how much of the original additive package is left is still well up, no fuel contamination, no wear evidence.
BTW two of my cars in the U.S. has a 7500 mile change interval. the same vehicles, same engine, same oil recomendation in europe has a 15,000 mile (well, 25,000 kilometer) change interval. I suspect they figured U.S. customers would never believe that number. But extrapolating the oil analysis results at 7500 miles give more than 15,0000 miles for oil life.