Welcome to Car Talk.
Is your van still under powertrain warranty? Has the PCM been flashed to the latest version of the software (may not apply to your vehicle; check with your dealer)?
Why were the coil packs replaced?
You should be able to direct heated air to both the windshield and your feet at the same time.
Actual winter tires make a big difference. Do you have a set?
Your van uses the same V6 engine as the Durango, with slightly lower horsepower. But it weighs less than the Durango, so you would need to go with the Hemi V8 for better performance. Fuel economy would be lower.