Need some help diagnosing a climate control issue
 

I've got an '01 3.0 and am having issues with heating and cooling. When running the AC, it behaves as if it may need a coolant charge, which I can have checked. When idiling or sitting at stoplights, it doesn't blow very cold, then gets colder when up to speed. When running the heat, it behaves as if there is a thermostat issue -- basically, not blowing warm air when sitting at stop lights, etc., but heating up when at highway speeds. I suppose it could be both of those things, but was thinking they may be related. Any ideas before I take it in for a look?

The blower works fine, so it's not the Final Stage Resistor Module.

This is a relatively common problem. Your aux fan needs to be replaced. There was a recall for this part in 01, so make sure your vehicle has had that performed.

Just got of the phone with a dealer here in Denver. He told me there wasn't a recall on my '01 -- confirmed the aux fan could be the issue and quoted $800-$1000 installed. Any chance this could be a DIY -- i did the FSR Module myself. Hate to drop a grand on this. Thoughts?