i just ripped the center fin off of a 5'8" webber gutter lover i had been riding i decide to get a new board for winter and went up a few inches, something that would be easier to paddle in a full suit i got a 6' 3" COS super stock. Im having problems with turning and pumping on the board. will i just eventually get usto the board or is it too big for me?
A 6'3 PSB might be a bit big for average surf at your height and weight, but like wonton said, you might appreciate the extra float in your winter suit, in heavy, overhead winter waves. There's certainly something to be said for keeping a "winter board" in your quiver. My standard recommendation for that board would be from about 155 or 160 lbs up to about 190, depending on your age and fitness level, and type of waves you ride.
Switching up fins is a good idea for loosening up a board that feels too big. Three things to consider fin-wise are an overall smaller fin... a more upright fin with less rake... and a fin with more flex. This will help most in smaller, average surf. In bigger waves, you might want to stick to your standard fins, and get used to the feel a bigger board gives in bigger surf.