Just in the last week or so I've been noticing my temperature gauge doing different things. I know the stock gauges are glorified idiot lights, but here goes anyway.

The truck has always run with the needle below the word normal on the gauge. The last couple of weeks it has started running right in the middle to sometimes all the way to the "a". It only does this driving surface streets. On the highway it stays below the "n".

The thermostat is less than 6 months old.

 

Sounds like your fan clutch is worn out.

 

How do you test that part?

 

I believe there may actually be a proper method to test them, but I don't know what it is. After years and years of wrenching for a living, I just know them by feel. The fan should offer up resistance when you try and spin it by hand. If you can spin it with your hand and it makes more than 1/8th of a revolution after you let go, it's bad. If there are any signs of oil leaking from it, it's bad. The hotter your engine gets, the louder you should hear the fan 'roar'. If it never gets very loud, it's bad.