Why would the temp and fuel gauges peg over max and the tach not work properly

The honest answer is that without testing the signals, there is no way to know. The temp gauge may have been damaged and causing the gauge to peg. The fuel gauge should not have been affected, so that tends to point toward a possible gauge cluster issue. Without more data, that's about all I can guess at this point. It is an OBDII computer vehicle, so a shop with a scan tool should be able to test for signals & gauge operation.