Need some help diagnosing a climate control issue

[CysMyGuy]

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.