These last few days my truck will sometimes go more then half way over to the hot side then will come back down an then it will go to the half way mark or a lil pass it then fall right back where it should all this happends fast..im going to put a thermestate in it to see if thats it but this is a new motor it's full of fliuds an all. what dagree thermestate should i put back in her? or could this be a bigger prob cause i was thinking when t/s go out they go out

 

Could have some air in the system...

 

I had this happen last year in my 03 QC Hemi.
The temp gauge would go up and down almost "pulsing" in 3-5 minute intervals.
I replaced my T-stat and all was good.
On inspecting the T-stat, the rubber O ring was pinched for some reason???
Anyhow, with your mods, definately look into a 180 degree T-Stat.
Get one with a "bypass". I believe Stant and Mr Gasket make a 180 for our trucks.
Don't expect them to come cheap., They are usually around the $30 mark.
Might also be a good time to flush out your radiator and replace the coolant.
Your gonna' lose some coolant anyway when your T-stat.
That's almost a complete service for your cooling system.
If this doesn't cure the problem, it could be your water pump?
Start small replacing the cheaper stuff,then go for the big stuff.
Hope this helps?
Al.