Hi Paul!
I agree with Mike.
For future cooks, you should start checking your racks of ribs for weight.
My formula......2 1/4 - 2 1/2 lb. slabs will take 6 hours at a grate temp of 225?. Anything above these weights and you are looking at more time.
Many folks cook the large inexpensive spares at the super stores. After trimming to St. Louis style, they can be over 3 lbs. and much thicker than baby backs or smaller spares. If this is the case, then 7-8 hrs. is more likely needed.
I have learned and traveled enough to realize that ribs come in so many different weights and shapes. In this part of the world, I have never, ever seen a slab of baby backs that weigh in under 2 lbs. However, many folks on this board cook slabs that weigh around 1 1/2lbs. Well, my formula will overcook them.
This is why it is so hard to "generalize" when it comes to cooking ribs.
So, start taking notes and recording your weights, cooking temps and finishing times.
Best of luck to you!