Is the shifting not as precise and smooth as before? The shifters has become stiffer? If the drive-train is in an excellent condition it is likely that the problem is caused by the inner and outer cable as they are not as efficient as before. Modern frames provide internal routing of the outer cables in the frame which complicates the work of the inner cables, which accordingly calls for more frequent replacement to maintain top performance. There are complete kits available to replace the old shifter cables or all other components. from tension regulators to internal cabling so as to completely renew and repair warn parts. As for the high range road bikes with the inner and outer Shimano, PTFE and polymers cables these are the secret weapons to an unattainable feeling against the other competing products.