+1 on the shorter cranks. My guess is this will help. What is your inseam and what size bike are you riding? This should help decide if you may need shorter cranks. If you are tall, then probably not, but otherwise shorter cranks could be the solution.

Also, keep cranking the seat up. You need to keep raising it until you feel yourself needing to "slip-off" slightly in order to reach the pedal at the bottom of the crank circle. At that point, you lower it a tad, and then your spot on.