I think you may be right on just time and technique. I have commuted 120 miles a week for 2 years now to work and just started short tours. 24 miles a day in 12 mile increments 8 hours apart is quite different than 70 miles over the 9 hours we did on our short tour. We took 10 minute breaks every 10 to 12 miles and at the top on long climbs. Being more pro active on standing for bumps and just accepting some discomfort is normal on longer rides should help.