The 3 that don't work as well are hooked up to the same system. They worked until I had to replace a couple. I have compared the replacement parts with the old parts and they are exactly the same. Water pressure through those 3 are so weak, that my lawn is starting to die, in those areas. Not quite sure what I should do!!??

Something may be clogging them. Have you removed the heads and turned on the system? You may find the culprits.