I'll second the saddle height. Quick story, I took the bike out the other day and was going along grand for about 10 miles when I felt the saddle lower itself. I got off and highered it up and within 5 minutes my bits were numb. I lowered it again and no more numbness. I must have raised it too high. Not sure if this is your problem but it might be worth checking. Mark the seat post and lower it little bits at a time. Little bits are about 1cm long!
