I posted here a few weeks ago about DD taking FOREVER to eat (45 minutes for 5 ounces) and always falling asleep while eating.
Funny story .... We had gotten some Dr. Brown's bottles from a friend, and she said they all had level 1 nipples in there. Well, I noticed that there was one nipple that was a bit thicker than the others, and DD would finish a bottle in like 10 minutes with this particular nipple. Further investigation revealed that it was a Playtex level 2. Apparently she's been ready for more flow for a long time.
We made the switch this weekend, and I have a MUCH happier baby on my hands!!