Happened to me.

Does it take a really freaking long time to warm up to a decent operating temerature? Your teg should have the temp needle somewhere close to the middle within 3 minutes from a cold start.

Thermostats just die every once in a while., and they usually get stuck either open or closed.

On the grad scale of 1=changing a light bulb and 10= rebuilding your own tranny, I'd say it's a three. Not a cakewalk, but if someone knows what they're doing, it shouldn't be difficult at all. Though, for the sake of the fact that coolant will get EVERYWHERE and it is not a job to do by yourself for the first time, you will want to either get a friend who has done it before or take it in. If you want to tackle it yourself, the Helms manual's a good place to start.