How many miles do you have on your bike? shifters usually last a long time....
If you have Campy you don't need to replace them; they can be overhauled pretty easily at your bike store. Not so sure about Shimano but pretty sure you would have to replace.
Be sure you don't have any "gunk" gunking up (technical term) the cable feeds under your bottom bracket. Build of up sport drink, dirt, dead worms and frog guts down there can impede shifting.