One night I went to take my truck for a drive and it wouldn't start, luckily I had the good ol NV4500 and just gave it a bump start like most people would, now I have excess of 80psi oil pressure at times and my coolant is always reading overheating. Thought nothing of it as well engine still ran fine so I put my money into other things like new long tube headers, now the coolant temp reads 255 with engine running and when its off the gauge goes back to normal temp (200) Ive never seen anything like this before and I dont understand a thing about it. Motor is freshly rebuilt (November 2020)
5.9 Magnum (360ci)

 

Is your coolant system full of coolant with no pockets of air in it? You can also use a laser temperature gun (readily available at auto parts stores or Harbor Freight) to check the coolant temperature at the upper and lower radiator hoses to get an idea as to its true temperature.

As for the oil pressure issue, might want to hook up a mechanical gauge to the engine to see what the true oil PSI is. It's not uncommon for the gauge or the sending unit to cause a bad reading.

 

What year is your truck? What oil pump did you put in it?

 

According to the profile it's a 95.
Does the temp gauge read 255 and then immediately drops when the engine is off ? Or does it show 200 with a cold engine and then climbs ?