My dad and I used to have a '93 F-150 project truck with a 4.8L engine. RPM's would jump randomly while idling, parked, and using the brake. It's common for 4.8, 5.3, and 6.0 L engines to do that. Not necessarily just a Chevrolet problem because I have never experienced it with our Chevy trucks.

 

Had the same problem with my 08. They replace slip yoke and not a bump since, I believe the replacements are chrome moly.