Val--It can take quite some time to fully degass a wine. I don't recommend manual degassing for fruit or grape wines that are not early drinking wines. I agree with what Greg said--that the cool temps can keep the CO2 from coming off and holds the sediment in suspension. Allow the wine to sit in a bit warmer environment. All our wine just sits in carboys on carts in the winery in normal room temp. They degass and clear by themselves. Nonetheless, natural degassing can take many months, but that's OK because they need to bulk age, anyway. You should allow all your wines to age for no less than 1 year. You'll be amazed how that year in bulk aging not only improves clarity, but also improves flavor because offending esters, bittnerness, etc. will fall free from the wine---but only if you give it enough time!
And if you are backsweetening, your wines need that bulk aging time because you can't sorbate cloudy wine and expect it to prevent a refermentation because there are far too many yeast cells present in the wine. The rule on sorbate is--only sorbate clear wine where the bulk of the yeast cells have been racked off.