How long are you giving him at the breast? Are you nursing one side or both or swithcing back and forth? What is his behavior like at the breast?
My guess is that you just need to give him more time at the breast - he will get faster but for now he may need a bit longer. And I'd second the breast compressions while nursing.
the Pediatrician and LC want me to limit him to 30 min total nursing each session to avoid caloric fatigue since he is a slow weight gainer. He usually goes the whole 30 and i have to pull him off. I am mostly nursing 1 side bc of green BM a few times when i switched between. And he is sometimes gulping at the breast, other times "nibbling" without any large sucks. Usually at that time i use compressions.
I will also add he had only weaned off o fthe nipple shield for a week now, maybe he has to learn how to be effective?