Toyota guages definately read odd.
I know mine sits in the middle from about 80degs to about 96 or higher.
To get it to move up, I turned the thermo's off, and watched the microtech readout.
It went to 98 before the temp guage had even moved, and by the time it hit 100deg, the temp guage had gone from middle, to over 3/4.
I then turned the thermo fans on, and within 10 seconds, the guage was back to normal, but the microtech readout took a good 45-60 sec to drop back to 84degree.
But, when I had the old thermo on there, it would get hot sitting at lights, and then take a good 30secs of driving to get back to normal
But even when the ecu readout would have been around the 100 mark, I didnt see any lack of performance, or any knocking.
You could just be experiencing some wierd factory ecu thing.