John, just to add some to Big Poppy's post. Start taking longer and longer rides. Being in shape and being in shape for a longer bike ride are not completely the same. If you go with a Corbin or other type seat, get a back rest to take some of the stress off your arms, legs and back. I don't "lean" on the back rest, but do rest up against it. Stopping often will help also.

BA has Freak, 160mains, 44pilots, air mix3 1/2 to 4 turns, BUBS dresser dogs. Never had more fun on any bike - 2nd bike 2008 RIIIT