thermostat not staying steady.

A little leak shouldn't but low coolant might. Re-check the level and make sure.

Is it just higher than usual, or is it actually fluctuating from low to high?

Changed mine... So far..no problems..
Hopefully you find the problem...

Could be fluctuating from the tstat opening and closing. Maybe you just never noticed it before. I've had vehicles where if I watched it long enough I could see the temp go down when the tstat opened.

Or, maybe there is an airpocket in the system.

Was the old one stuck open? These trucks should run between half and 3/4

Still have the oem ts tatami mine never gets to the 1/2 mark it's a 4banger if that makes a difference

Before changing mine it would barely reach 1/4 mark...
Now it runs at 1/2 mark... Never seen it touch 1/2 mark as long as I have owned it... Till the new AC Delco part went on...

Lets not talk about where the needed is on the gauge again.
That proves pretty much nothing. Some read 1/4. Some read 1/2, some read 3/4. If mine and yours are different it doesn't matter, could be for several reasons. The point...if the gauge higher than it used to be, or is it actually fluctuating?

I figured it would read higher. Mine old ts would get stuck open sometimes and throw the code. When i installed the ts i ran it for 15 to 20 mins to get air out i did it 3 different times just to make sure. I found the leak and fixed it. It would only fluctuate one degree mark when i was driving so i think as stated about that it is ts opening. I am going to keep a eye on it and check my coolant just to make sure i am not losing anymore. Thanks for the help guys.

Also get yourself a scan gauge so that way you know what temp it's running at. I've put LED's in my cluster and the needle has never been exact since, my scan gauge says it sits at about 170 on warm days and around 200 on hot days in traffic.

I'd like to hear about people's scan temps, maybe driving up the road.

2008 3.7l.
188/189 normally while driving. Max 212 in +100 heat with a/c and traffic.