I think I've really cracked it this time--sit high and tall, as if being pulled upward by a string attached to the crown of your head. This prevents slumping, slouching, shoulder hunching, etc. I adjusted my mirror so the view is perfect in what I perceive as the correct posture, if I look in the mirror and the view isn't correct I know I need to adjust my posture. Also, to make the knees happy, no mashing--start slowly from a stop, no need to rush to get up to speed. It's a cruiser, supposed to be fun and relaxing, right? I had a couple of days that weren't too windy and this seems to be working.
Thanks again for all the advice.