Aaron Dosentcare

I just got a 2006 Chevy Silverado z71 from my grandfather I've had it a week at most and haven't had any problems with it until today I was driving and while turning I noticed that it got real hard to turn so my first thought was the belt came off or broke so I pulled over and popped the hood and the belt is fine check the power steering fluid level and it's full there is no leaking or anything got ahold of my grandfather and he told me that it happened to him a couple times but he just kept driving it anyways and he said that after awhile it started working properly so I'm trying to figure out what is causing this to happen its still hard to turn both ways while stopped and while driving please help the truck has 116xxx miles on it