Check to make sure that all the plug wires are snaped on tight. I had this problem and is was a loose plug wire. Not so loose it fell off the boot, but loose enough to give it a skip at low idle.I have a 99 tahoe LT , Truck has a slight miss at an idle in cylinders 3&4,As soon as you get above 1000 rpms the truck is fine it's not bucking,or missing causing it to run like crap when driving it down the road, i have replaced the o2 sensor that was bad ,and egr valve gasket with the new updated gasket w/ screen, Me and a couple of my techs are thinking Metering body assy, Does not have any intake leaks also tested for that last week, Is there anything else it could be just wondering this is my first chevy SUV
Pull the boot up the wire and put the little snap collar on the plug then push the boot down. That way you are sure it is seated right.