That iPhone jailbreak app existed to trick the AT&T iPhone into thinking you were on WiFi, not 3G because originally AT&T restricted the use of the slingplayer app over 3G out of fear it would clog up their network (they later reversed that).
I suspect your issue is not that you are being throttled, rather that you are in an area that does not have a strong signal. If you go to Menu > Settings > Network > Signal Strength, what number is listed there? As I mentioned in the other thread, I have never had a problem streaming Slingbox over 3G and I'm a pretty heavy data user.
Have you tried updating your towers, *228? That might up your signal.