With a 195 degree stat, it should be right about 195 degrees. Of course, the sensors aren't exactly what I would consider "precise"..... so, you are at least in the right neighborhood. If it runs good, and gas mileage isn't horrible, I would run with it.

 

Wow, 15-18mpg on a 5.9 with 4x4? That is a dream mpg for most of us 5.9 users... at least for me. I get more like 10-14 mpg. I have similar temp issues with my rig. Runs normal temp when external temps are above 80 degrees. When temps are below 80 degrees, truck has issues trying to warm to temp. I hover around the first line on the temp gauge. My torque app shows around 150-160 which is too low and contributing to my low mpgs during winter season. My low temps get this low and sometimes lower if outside gets really cold and car is in forward motion. If I just let it sit and idle outside, it will eventually warm to temp "180". fan clutch works as intended. will free spin after a brief interval. I have to find something and cover about 1/2 of my front radiator area to get it up to temp when in motion during the winter season. I have no issues with summer. Actually the truck can overheat in summer if I lose my electric fan while using AC. This is at idle. Will cool just fine while in motion. Cannot get a consistent temp year around without manually intervening during winter season. lol. I assume the 180 stat I have just does not completely shut off the flow during winter time. I have changed the stat several times during my lifetime ownership of this vehicle. Switch different brands, etc. None of them addressed my low temp issue during the winter season.

I will have to check the timing chain to see if that is loose or not. The 5.9 still runs strong and runs smooth. So if timing chain is loose, I assume engine will run sporadically across the rpm range. So far, I do not feel anything odd from the 5.9. Will get it inspected next go major tune up go around.