RE: How often??
Check your ATA measurements. It's a good rule of thumb to change the string/cables every two years although todays strings/cables can last longer. I know my 2001 Vortec I sold my buddy has the factory string on it. I'm making him new ones this year!
I've made a string for my 06 Ally and need to make cables now. My ATA is out of spec, string/cable crept.