This really could be over-active let-down showing itself in a slightly
different way.  I think it's very common for babies dealing with heavy flow
to pull off a lot as if to say " hey let me catch my breath here".  Is mom
feeding from both breasts at each feeding?

Since  the baby is really gaining well, you could try the standard
--feed from only one breast per feeding
--let some of the heaviest MER, usually the first, spray into a towel instead
of babies mouth
--reposition so that baby is higher than the breast--have mom lay back in a
recliner or on pillows and then put baby on top.  Gravity can help him get
some control over the force of the milk.

If this is over-active let-down, babies dealing with this can sometimes get
pretty ticked off and start fighting more if things don't get a little easier
for them.

I think it is also common for these babies to be "gassy" because they can
swallow a lot of air with that heavy MER and are sometimes having to deal
with lots of foremilk.  (and that gets into that whole lactose digesting
enzyme thing which I don't have tons of knowledge about)

Hope this may be helpful

Kim PA-C, CLE in P.A. where it finally rained and is getting cooler