I am having similar sync problems with new iPhone 4s and latest iTunes.
At first iTunes recognized my iPhone, but sync was so sluggish it was taking hours to sync a few apps, and only got a few on there. i- tunes diagnostics wouldnt work at all. Whole thing was hanging. WHen I disconnected phone iTUens returned to normal. I was using cloud for back up.
Rebooted, reinstalled i Tunes, stopped all start ups except essentials, now diagnostics works but i Tunes wont recognize my phone.
here's what i got
Microsoft Windows 7 x64 Home Premium Edition Service Pack 1 (Build 7601)
Acer Aspire 5534
QuickTime not available
Apple Application Support 2.1.5
iPod Updater Library [Error:0000000D]
CD Driver 188.8.131.52
CD Driver DLL 184.108.40.206
Apple Mobile Device 220.127.116.11
Apple Mobile Device Driver 18.104.22.168
Gracenote SDK 22.214.171.1244
Gracenote MusicID 126.96.36.199
Gracenote Submit 188.8.131.52
Gracenote DSP 184.108.40.206
iTunes Serial Number 0042ADD402FE4340
Current user is an administrator.
The current local date and time is 2011-10-23 15:15:22.
iTunes is not running in safe mode.
WebKit accelerated compositing is enabled.
HDCP is supported.
Core Media is supported.
Video Display Information
ATI Technologies Inc., ATI Radeon HD 3200 Graphics
**** External Plug-ins Information ****
No external plug-ins installed.
iPodService 10.5.0.142 (x64) is currently not running.
iTunesHelper is currently not running.
Apple Mobile Device service 220.127.116.11 is currently running.
**** Device Sync Tests ****
No iPod, iPhone, or iPad found.