Climate control becomes unresponsive

I have a 98GT with the dual auto climate control. I've noticed that the climate control will work perfectly for about 20 minutes and then it becomes unresponsive. I'll set the temp at 23 and after about 20 minutes of driving I'll notice that the interior temp is getting colder, so I add a degree or two on the climate control and nothing. It remains at the low blower setting until I turn the heat all the way up, as soon as I turn it to the max, it comes on full, but doesn't always blow full. It's wierd, you can clearly hear the blower on full, but the air that's coming out is definitely not the full flow. If I leave it this way then the airflow out the vents will eventually pick up to full airflow. I've read through the messages on climate control and nothing seems to fit this problem.

Any ideas would be helpful as I know that I'd be charged an arm and a leg just to diagnose the problem, let alone fix it.

Those heater controls are known to be problematic, and is more than likely what is causing your problem. The factory part is expensive, so check e-bay.