Originally Posted by
Jamminatrix
As for your comment about "shifters seem to take a fair amount of effort", this is a sign of worn/old/dirty cables. Shifters with higher mileage just get 'sloppy', but they should not get 'heavier' in action.
If you decide to replace the inner shift wires also consider installing new outer housings as well. The wires wear themselves into the housings and the new wires may not play well in the existing wear patterns.