Motor temperature gauge is not working

This is totally normal. All radiators contain an antifreeze/ antiboil component when filled as per manufacturers instructions. This stabilizers the temp of the coolant, reducing fluctuations in temperature. The thermostat is heat responsive. Basically a piece of spring steel heated to a temperature then cooled, so as to retain the memory of when to react. Replacing the water temp sensor on this occasion was probably unnecessary, tho in saying that, I have replaced mine & friends with beneficial results.

I would suspect the thermostat first.

It may be the sending unit in the tank that needs replacing. Here's how you can check: Turn the key on and disconnect the sender unit at the gas tank. Ground the sender unit's wire with a jumper wire from the truck's harness to ground. Watch the gauge. If the gauge on the dash is good, grounding the sender wire will cause the gauge needle to react and should move to full. This would indicate a new sending unit is required. If the gauge doesn't move when the sender unit is grounded, the gauge is bad and needs replacing. Pull the instrument cluster out to replace the gas gauge. Likely any old ford gas gauge might work-back then, there were not so many production changes.

connection on the back of the dash needs cleaning if you push on the dash and it all works then this is the fault. sometimes hitting it works just fine for awhile but not to hard.

Defective hose?

It appears the cap screws off? It doesn't look like a regular radiator cap. I looked at acdelco parts book.
If the cap is stubborn, cold engine, sometimes I use a pair of pliers with wide jaws, grip the cap and screw it off. I haven't seen your type cap, before. If this was my vehicle, I would certainly want to look in the radiator. I'd get that cap off, one way or the other. Of course, nobody wants to damage anything.

You have blown a fuse..check fuse box. There may be one fuse box one in the cabin but also check for the fusebox in the engine compartment.

FLUSH RADIATOR, HEATER CORE AND ENGINE BLOCK.ADD 50 / 50 ANTIFREEZE AND WATER ALSO REPLACE RADIATOR PRESSURE CAP.IF TEMPERATURE GAUGE STILL STAY HIGH THE ENGINE COOLANT TEMPERATURE SENSOR COULD BE FAULTY.

I would either go to a shop or buy a Infrared Thermometer and check the temp of the radiator and the upper radiator housing temp, that's a nice car and expensive to repair, but to blow the engine it would be worth nothing

Water Temperature Indicator Sender Unit
The water temperature indicator sender unit is installed on the engine into an engine coolant passage. The water temperature indicator sender unit reacts to the engine coolant temperature. Its resistance decreases as the engine coolant temperature increases.

Water Temperature Indicator Sender Unit Removal
CAUTION: Do not mix Standard (green) Coolant with Extended Life Coolant (orange). If mixing occurs, drain engine cooling system and refill with originally equipped coolant type. If this contamination occurs the service change interval on Extended Life Coolant will be reduced from 6 years/150,000 miles to 3 years/30,000 miles.

1. Partially drain engine cooling system as described.
   

1. Disconnect engine control sensor wiring (12A581) from water temperature indicator sender unit (10884) .
   

1. Remove water temperature indicator sender unit.