Hello, I don't mean to take over this thread but I believe I have some useful info.
I followed Benjie's earlier link and researched bitsnbolts.com, which was very interesting. That led me to NVFS updates available at
www.Palm.com. I checked that out, which was fruitful since it had the Treo 650 Updater 1.13 for Sprint PCS, and I was on version 1.12. I followed the whole process, which included a hard reset, with success. Afterwards my device runs much much better with no unintentional reboots.
My advice for these symptoms/problems is look at support under Palm.com. Good luck!