From your original post / question I'm guessing that 1800 miles could be done in 3 weeks, give or take a day.
I'm similar in cycling background to you (though probably older at 56 y.o.). Started taking the month of September off and taking a long solo ride / tour four years ago. I typically do between 600-700 miles a week though I've had days when the wind was up that I maxed out at 50-60 miles. That said, I'm pretty well beat at the end of every day in a way many people would equate with the trip being a grind rather than a pleasure. We all do this for our own reasons and my reasons have a large component of the trip being a physical challenge.
I don't see anywhere on your post how much weight you're carrying and weather you are camping. I primarily "credit-card" tour and sleep in hotels and eat in restaurants and ride a Ti road bike so my entire rolling weight (except water) is around 35lbs. Thats not a big shock to the system the way going from a racing bike to a touring bike w 30 lbs of gear would be. There's a excellent article on packing light over at Crazy guy on a Bike by Pete Staehling (sp?) who answered your post a couple of spots ago, I suggest you read it.
Also if your camping/ cooking you have a smaller daylight window to ride in although that's somewhat offset by the fact you can camp at many more places than you can find a hotel.
One thing that I had to get used to mentally was that if you got a big wind in your face, there's a real good chance you will be dealing with it ALL day (& maybe for several days on end). Previously to taking up the touring rides I would ride a loop or an out and back ride where the wind would only be against you for one part of the ride.
Lastly, I'm not much of a social sort either and a big part of these trips for me is the hours on end of a clear head but as others have noted, some of the people you meet the way really adds to the trip. And it's all completely effortless. It may just be someone in the booth next door in the diner, the guy who runs the rural hardware store where you're trying to cobble together a fix for your stuff, or someone at the top of a pass where you've stopped to change out of your sweat soaked jersey for the big descent, these little 10 minute conversations end up being some of the trips highlights for me.