Sounds like your vine is slowing down, ripening its fruit, and getting ready for the big rest. Being in a container restricts the vine's roots' foraging ability so it's not too unusual to see your plant coming to a timely end. Leave the pumpkin on the vine until the leaves are dead. If that doesn't happen before Halloween week, pick it and carve it up anyway. If you're not eating it, it doesn't have to be completely ripe. You can leave it on the vine after the leaves are dead if you prefer since you won't be getting any hard freezes in SoCal.