1999 chevy silverado that seems to rev. to high

my dad just bought a 99 chevy silverado with the 4.8 motor and the engine revs really high on idels 1500ish and above.....

is that normal? it never seems to get below 1200ish to 1000ish

It's not normal!
you have a problem, look the engine over closely for a vacuum leak such as a loose or disconnected hose, and spray carb cleaner around all of your gasket joints on the intake system. If you hit a leak there should be a sudden change in RPM. If all this fails to locate a problem then take a look at the air control valve, located at the throttle body for a loose mechanical connection. This is about as far as you can go without actually back probing electrical connectors and trouble shooting the PCM (power control management) system.

The problem could be a simple vacuum leak, or more complicated problem like a stuck pendalent inside of an air control valve, or a bad sensor somewhere.

Make sure you closely examine the air duct between the MAF sensor and throttle body, this needs to be a tight system any leaks in this area and the MAF signal becomes false and the PCM chase's it's tail.

Enough rambling, give it a shot

Good luck!