As I've found out this past weekend too, too low of thermostat can cause issues as well. My heat used to get too hot to the point where I had to turn it down less than halfway through a trip. I replaced the radiator with an Aluminum Honda half, and put in a 180 degree thermostat in place of the 192 degree unit that had been put in about 5,000 miles ago. My Galant runs too cool now. According to the logger, didn't get a touch above 180 degrees Even after heavy boosting.
I'll be putting a new 192 degree thermostat back and hope the heat works well after that. Anything less than 190 coolant temps, our heat seems to really suck from what I've found so far, so you might give that a shot.
If your radiator fan is wired to run all the time, that could be keeping the coolant from reaching optimal operating temp as well. In the winter when it is cold, it will have more of a negative effect than a positive effect.
With all that out of the way, if the heat still doesn't work well, then I would dig into the dash. Best to get the simple stuff out of the way, then go for the heater core lines and such. Autozone is bad for giving out 180 degree thermostats saying they are stock replacement. Ours come factory with 192's. I've had bad experience with Advance and Autozone t-stats as well where they started sticking after about 7-10k miles. I've had great experience with Napa's however.
