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1999 GMC 6500, 454 gauge showing hot but not

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I have a '99 6500 with the 454.
It's got aprox 70k on a GM rebuild engine, been well maintained for the last 12 years, has 180k on the truck.
It started showing hotter than usual, when shut off and restarted the check gauges light would come on, temp up around 210 and then it would come down after running.
It started heating up to 210 quickly in 3-4 miles from cold, not normal.
If left idling it will show 220+, if you rev is some the gauge gets jerky and will come down.
I checked the temp with a scan tool and it agrees with the dash gauge (that means the dash gauge is ok), a thermo in the rad says 180, lazer heat gun shows the same or cooler at the goose neck so it doesn't seem to be hot, doesn't feel hot.
Seems this only has one temp sensor (in the right head), it doesn't have a separate gauge sensor?
If I could find a separate gauge sensor i would bet that is the issue but can't see one.

So I changed the temp sensor and thermostat, no difference. The fan clutch seems good (tight).
I went ahead and had the radiator checked out as it's old but it's clean.

Wondering if anyone has a good idea why it's showing hot when it's really not?

Let me now your thoughts/ideas as I am running out of my own.

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