I have a 1997 GMC with a 305 vortec v8 the motor revs at 2000 - 2500 hot or cold i have changed the plugs plug wires and checked all the sensors do you think it could be the dome gasket?

An air leak at the head can cause reving at idle. When you changed the spark plugs what did the old ones look like A light gray or white color would indicate a lean condition. This could be a head gasket or a leak in the intake between the injection system and the intake valve.