5.9 Magnum Question

I was handed a 2000 Magnum,for free... even the service replacement heads,were toast,the roller cam,had three flat lobes...Ended up with EQ heads,the Crane cams,stud set up, and 1.5 Comp Cams Chev rockers...I like valvetrain adjustability,on my stuff...
Tim , how does a roller lifter eat a cam, no oil ? High miles?