Hi Big Ir!
Yes I do cook mine for 8-9 hours. I think the biggest difference is the type of spares I used to buy. They are the large Bronto spares that weigh around 4-5 lbs. per slab. These are the types that many stores have sales on for around $1.00/lb.
They are very large and just take a long time to cook.
I have been cooking almost all baby backs lately and they continue to take 6 hours. These weigh 2 1/4lbs. per rack and are very thick and meaty, hence the long times.
I learned all my rib cooking techniques from cooking on the MIM circuit. The folks who shared with me, use large water smokers(Jimmy Maxey designs) and cook at a constant 225? for 6 hours. We all buy our baby's from Sam's Club so the meat is consistent.
Now, when I cook these, I usually do 6 racks and of the 6 racks, 2 will come out like yours did...many shiners. The others are the ones I choose to turn in.
Big Ir, you are not the first who has had very different results when cooking ribs. All I can think of is the size and thickness of the ribs used. OR, perhaps the ambient climate? Not sure what else it could be.
Sounds like you are close to perfecting them, so keep good notes and eventually you will nail it.
I am cooking another MIM tournament this fall...Sept. 13 & 14 in Macon, GA. I will further validate and look for anything new to report.