Its a 1995 setup. You should do the CS 144 mod instead of having that old POS rebuilt. Temp gauge at full you need to check your Gauge temp sensor on the rear of the block.
Ground the lead and see if the needle deflects. Pic here:
The dancing is because you have put a power feed too close to the gauge power wire and you are coupling the power to the gauge. Reroute your radio power. For both your radio and CB you need a ground; ideally a strap' from the case of each to the nearest body point to ground them. Power and ground if run together should be twisted at least 1 1/2 turns per inch. More is acceptable.