2000 Chevy blazer is acting like it is lunging on hwy mechanic has changed the distributor and fuel filter along with the spark plugs but car still has the problem Any ideas?

The PCV valve may be stuck open which will allow too much air into the intake. try replacing the PCV valve its only about $5. it is located on the top of the drivers side valve cover and is conected to the air intake by a hose.