Before buying new parts, have you tried lubricating the cable? I use a cable luber and Maxima Chain Wax on cables. Here's a decent luber:
http://www.ebay.com/itm/Motion-Pro-C...98f9d5&vxp=mtr
Lubricating the cable can make all the difference.
Once the cable is lubed, shoot for about 1/4" of freeplay gap, as measured between the hand lever and the perch it is mounted on.