running hot/air bubble?

[RuralRoute C-30]

Its been a week since replacing the front & rear seals, then the gauge cluster to get the oil pressure issue figured out.

Now the temperature gauge is running at 3/4 to nearly the red line before the thermostat reacts. Before all this it ran around the middle of the gauge.

Tonight I installed a new 195 degree thermostat, sending unit to the gauge too. Also redid the wire to the sending unit. (when taken off the gauge is sends the gauge to '0'. Even took the gauge cluster apart, (good at that now! and swapped the temperature gauge with the one I was using before all this gauge cluster repairs).

Same thing, gauge doesn't take any time at all to start rising. Reaches 3/4 hot and then the thermostat lets it run to the red and come back down again to around the 3/4 mark.

I read an air bubble in the system might be the cause. Any input on that?

Since the front & rear seal and timing chain was replaced it hasn't been driven more than 20 miles at the most. Now I don't want to take it too far until this is figured out.

Water pump? It is all that is left to replace. No leaks or noise there though and used the old one after the front seal and timing chain was installed. (mistake #?)

Appreciate any input. What is normal for these trucks to run temperature wise? Is the idea of an air bubble a valid one? No sign of water in the oil either. Just suddenly has developed this new "hot" personality!

I swear it just craves for the attention!

Appreciate,
Mark