First thought: Having a good plan and managing your time well over the next 105 days is going to be very important (but you already knew that).
The wife in I moved and downsized four years ago. Our move this time was only 50 miles, but we had made several much, much longer moves earlier in our lives. The process is quite similar regardless of the distance.
Regarding your "stuff", your primary options are to throw away, give away, donate, sell, or move. Those are obviously personal decisions and you'll likely do some of each. In my experience a major move can be a great time to pare down your belongings if there's a lot.
How much "stuff" are you looking at? A 5000 sq. ft. house where you've lived for 40 years? A 1200 sq. ft. condo that you moved into two years ago?
Do you already have a permanent home lined up in Colorado or will you be renting?