I have this problem too...or at least, I do now. A day in 'shopping mode' is more exhausting than a day of working on our farm! This never used to be the case for me, though. I used to work in retail, so I'd spend 5-6 days a week for 9-10 hours on my feet and basically walking slow. I was used to it. I'm not anymore (thank goodness!).

I really think it comes down to conditioning. Walking slowly is a totally different way of using your muscles than walking fast, or jogging, or hiking, or biking. I think that if you did it every day, you'd get used to it and it wouldn't tire you out as much.

I can't help with the boredom factor though!