Well, I'm also having the .3 upload cap happening on my Streak. I flashed Nandroid back to a couple of old versions of StreakDroid and SimpleStreak, but no change. I was also getting terrible download speeds (about 500kbps or so). Probably unrelated, but it began occurring after I came out of contract on AT&T.
I did go into an AT&T store and replace my SIM with a brand new 3G SIM. It did work a little. My downloads are back to normal (2Mbps - 3Mbps). But my upload is still horrendous. I put my brand new SIM into the and HTC something or another and it base lined the expected 2.5Mbps down and 1Mbps up. So, it's not my account.
My next step is to flash the 353 recovery and PKG. Test, Root, set ro.ril, Test. And hope for the best! If that works, than I will flash 1.9.1. Might be an issue with the kernel overclock or usermode.
Of course, my best guess is that I royally pissed off my Streak
Hopefully it is not a hardware fault.