P0128 trouble code- thermostat?

I have a 2001 3.4L 5 speed 4x4 that I got about a month ago. I just got an ultragauge, and when I plugged it in the first thing it showed me is that I have a P0128 trouble code. P0128 code is "Coolant thermostat (coolant temperature below thermostat regulating temperature). From my research it seems like that is most commonly cause by a faulty thermostat. The only related thing I have noticed is that occasionally the temp gauge on my dash will jump up to way higher than it should be, and stay there for a couple minutes before dropping back down. Would that indicate that it is a thermostat issue, or something different? I don't have a whole lot of experience with engines, but I'm trying to learn as I'm on a pretty tight college student budget. Is this something that I would be able to tackle myself with little experience, or should I suck it up and take it to a mechanic? Thanks everyone for your help!