First a little about the truck 1996 2500 club cab long bed 4x4 142,xxx 5sp.

About two weeks ago I was driving to the next town over and noticed my engine temp gauge was up a bit higher than usual. It wasnt overheating so I wasnt worried. It was at about 190*, so i figured id watch it just because i hadnt seen it that high yet, (only had the truck 2 weeks) it hit about 190* even, and then slowly began to come back down and stopped just at the lower mark on the gauge. after about a minute there slowly climbed back up to 190* then stopped. This continued for another 10 miles or so. I turned the truck off, slightly concerned. Came back 2 hours later and didnt happen again until..... this evening when I was driving I-5 from portland i did the exact same thing! It went on for a half hour until i stopped for fuel. started the truck up and didnt see it the rest of the way home. other than the gauge jumping around didnt notice anything unusual, and im not too concerned i am just wondering what might be going on. I thought maybe the thermostat was getting stuck?, but i figured it would overheat? any ideas would be much appreciated

 

Its normal t-stat opening and closing.

 

Thats what i thought, but its doesnt act like this very often. Just thought maybe there was something else going on

 

It depends on town vs highway and load on how high the temp goes and how much it fluctuates.
Be glad that it fluctuates, if it didn't it would overheat with a big load.
When it doesn't fluctuate driving around empty then start worrying.