I wasn't sure if my experience might be informative but then read Mlackie's post. On AT&T, I was seeing quick toggles between UTMS and HSDPA. When doing 3G data transfers, I'd get the search to cut in and out. Maybe weak signal strength shown by the toggling has something to do with the search toggling?

First, this was with 2.3.3 OTB then with 2.3.4 OTA. For kicks, I tried AOSP Master, but wasn't able to get a data signal through.