3G High CPU utilization when waking iPhone

Recently gave my iPhone 3G to my wife, restored it to a new phone, then synced it with her information, music, applications, etc. She previously had used an iPod touch, and basically was trying to upgrade her to an iPhone.
The phone worked fine when I had it. I only had a short time with this specific phone as it was replaced under Apple Care about a week and a half before turning it over.
Now it pretty consistently is unresponsive when trying to wake it. By bringing up the System Activity Monitor App as soon as possible after powering it up, and leaving that app active when putting it to sleep I can see that the CPU gets slammed for a while during initial startup and has a significant period of very high CPU when waking. At this point I believe the cause of the unresponsive behavior is that the CPU is maxed out doing something.
Ive compared the running processes to an iPhone 3Gs and they were identical except the 3G was missing the MobileMusicPlaye until I brought up the iPod on that phone.
There are 2 things about the initial setup of this phone for my wife that are causing me some concern;
1) When first connected to iTunes after the Factory Reset I was prompted to restore an older backup than the iPod Touch one I took right before the swap. I didnt realize it at the time and accepted that restore.
2) I was prompted to upgrade and followed through with an upgrade to 3.1.2 after the Factory Reset even though the phone was at 3.1.2 before the swap.
At this point Im thinking about doing another Factory reset and set it up by sync only (no restore) but not looking forward to the time investment that will take.
Any ideas on where the high CPU utilization is coming from on wake? Is that a reasonable theory that the high CPU is causing it to be unresponsive when first woken up.
Any other insight from others that have been through this?
15" MacBook Pro Core 2 Duo Mac OS X (10.5.8) 2.6 GHz 4 GB RAM