I'm having a similar problem with my Droid X Sling Box app. I am using a S/B AV and my Droid X Slingbox app worked perfectly. And now after upgrading to version 1.2 a short time ago, the app hardly works over 3G. It still works over wifi.
I found out what the problem was. The new bottom menu defaulted on "HQ Quality" instead of "SQ Quality." Try SQ Quality. Mine works prefectly now, just like it did before the update.
Got this info off earlier thread.