Could be an app not playing nice. My wife has one on her tb that causes a reboot from time to time. She just won't remove them one by one to find it. But she's not rooted. Fast boot does some weird stuff too. I would still look at an app that may not work well with the tb. Some of them I use to use just don't seem to work right on my tb.
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Device: MyTouch Slide *ROOTED*