Peterbilt Problems

Hello everyone, New to this and this is first thread.
I am working on a Peterbilt PB348, the engine is a PACCAR PX-9, ILS 9 Cummins. Engine number is 74178846. To the best of my knowledge this truck started with a shift problem over 2 years ago. It then developed into a check engine light still with a shift problem, NOx sensor not responding. Long story short I am now working on this problem that has developed into a: 1. Red light in the DEF gauge. Derate in 25 minuets, 4 different coolant level sensors codes, and a no start condition.

So, I put new lines in for the fuel system and now it starts. Replaced the DEF quantity/quality sender/sensor. Cleaned the exhaust filters, Checked the doser valve for spray pattern and quantity. It seems to be within spec., replaced the NOx sensor (this elevated one code). Replaced the EGR valve and pressure differential sensor for the EGR, cleaned all the passages. Replaced the DEF fluid filter. Replaced the coolant level sensor. Replaced the coolant level transmitter. Traced and ohm 'ed the wires from the sensor to the transmitter, from the transmitter to the ECU. Have tried numerous times to reset the Derate, and codes:
1, SPN 111 FMI 4 Coolant level sensor 1 Circuit voltage below normal or shorted to low source. Low engine coolant level detected at the engine coolant level circuit. Flash code 196.

2, SPN 111 FMI 3 Coolant level sensor 1 Circuit - Voltage above normal or shorted to High source. High signal voltage detected at Engine coolant level circuit. flash code 195.

3, SPN 111 FMI 18 Coolant Level data valid but below normal operating range- Moderately sever level. Very low engine coolant detected. Flash code 197 or 3366

4, SPN 6303 FMI 3 Engine coolant level 2 Sensor Circuit-Voltage above normal, or shorted to high source. High signal voltage detected at the engine coolant level 2 circuit. Flash code 4865

I have run out of things to check other then start replacing wires.

If anyone else has any ideas, please let me know. This truck has been to shops out in town and still no joy with fixing this. Thank you, Orange Cat.