The Nissan Path

This is my first post, so hello to everyone.
I own a '95 with approx 350,000km on it and it has been such a great truck. It has been in the family since new and well cared for. Other than a little rust and the typical odometer falure, it has only required regular maintanance.
So the issue I have with it now is that the engine won't warm up to normal opperating temp. The needle stays close to the bottom of the guage, not the middle like usual. Could this be a dead thermostat?

yup! u go tthat right!

are you strictly relying on the gauge or have you checked the under hood hoses for temp? does the heater not work either? have you checked your coolant level?

I just replaced my water pump and thermostat and my gauge reads lower than it used to. I wonder if the napa thermostat (170 degrees F) is no good? The picture shows where the gauge is if you drive around on flat land, the green is where it will go if you are climbing a decent hill, and the red is where it used to be most of the time. (the gauge may read a little less after being driven only 15 minutes)