If part of it was hot and the rest was cold you may not be all the way warmed up.
My 2.9s take at least 3 thermostat cycles to completely warm the engine to 195 degrees.
There's another thing that might contribute is you say you put in a 180 degree? IIRC the spec is 193-197.
You can check it in the driveway.
I block the wheels and all the safety stuff to keep it there.
Slip a piece of cardboard over the front of the radiator, not big enough to completely cover it, but mostly.
Run the engine with the rad cap off, if its not completely full right now that's good, less spill chance.
Watch the fluid flow as it warms up, it should start at a trickle, then more and stop when the thermo closes. This should happen 2-3 times with a 195 thermo.
When the coolant reaches the temperature of the thermo opening it should flow steady, check your gauge.
Pull out the cardboard and let the engine cool a bit before you shut it down.
If at any time is starts to boil, you'll know, clear the cardboard and cool off. You can overheat doing this! So pay attention to the temperature as you are there.
This tells you several things:
Thermostat is working.
Water pump is working.
Radiator is flowing air and water.
Where your gauge reads relative to thermostat cycles.
Where your gauge reads at normal temperature.
I do this with cap on to test a repair or for the same reasons as above.
Another one, does your radiator flow air? They clog outside as well.
Sorry for the novella . . .
Good luck
Rich
Good luck