I have the Vibrant which is a very similar phone from TMob. Their Froyo update was made available 2 weeks ago. I installed it last Friday. Upon installation, I discovered that my paid apps including Sling were missing. They magically reappeared today.
If your update gave your phone a new build number, your carrier must communicate that information - its called a fingerprint - to Google. Otherwise, certain paid apps will not will not appear in market even if you own it.