I noticed the same cold spot on my 01, I had my door panel off once to replace the drivers side mirror but I made sure the plastic was put back properly and I used tape to re secure it.
I think it's just a design flaw on the 97-01's because the space between the door and the door jamb is fairly big even with the weather-stripping properly in place.
It's as if the doors should have been fit tighter or bigger weather-stripping should have been used, this wouldn't be a problem and I'm sure most people wouldn't notice it if they live somewhere where it doesn't get very cold, but we have had a few days of -40°c with the wind chill and that's when I would feel a slight cold draft in that area.
Thankfully the heat works great in my truck to negate the issue.