Jesse Burk

hey guys, im fixing all the issues on this vette i just bought. On the instrument cluster, the oil temp and oil temp gauge dont work. and the tach goes from zero to 6k and back to zero when i start the car.

I replaced the coolant temp sensor, and the oil temp sensor near the oil filter ,and the 2 oil sensors on the back of the engine near the distributor.1991 L98 automatic. i got a new tach filter from corvette central, but it doesnt look like the original ( little black box) so i havent installed it yet . Before i send mine out to get get repaired, or replaced,what else can i check ?