So, after reading the relevant messages over and over and over, I took the roast out a couple of hours before starting to cook it.
I had only salted and peppered it while it was waiting in the fridge.
I set the timer and pushed the probe into the meat and put it in the oven. It was 3:30. Figured it'd take about 2 hours cause the roast was a little over 8 lbs.
Started it in the hot oven and then turned down to 325. Checked the thermom/timer about a half hour later. GASP. It said the meat was now 90+ degrees. I thought perhaps it was so high because of the initial hot oven period. Next time I checked it was 115! It had been just under an hour. Freaked out. Put my oven thermom in to check the oven temp. 325. Suddenly realized that maybe I'd put the probe in a place that wasn't deep enough. Took it out and repositioned it.
Temp went down to 60. Whew. Kept checking it and, when it got to 125, I took it out and tented it with foil.
It turned out fantastically. This was a Costco rib roast and I was a bit worried about it since last year somebody said (in the Chron or someplace) that the Costco beef was a bit "livery" tasting. This was not true of my roast.
We had a potato gratin with shallots, a great salad my sister brought made of chopped celery, Italian parsley, chives and tarragon, an arugula and mixed lettuces salad with fuyu persimmons and goat cheese, and some delicata squashes filled with wild rice and pine nuts. We ate like pigs.
For dessert I made my new favorite tart from J. Oliver's Kitchen cookbook - ricotta, mascarpone, lots of grated orange zest, egg yolks and sugar whipped together. Stiffly beaten egg whites are folded in and the whole mixture is poured into a pie shell that has been baked blind. Then chopped bittersweet chocolate is scattered on the top. Lastly, strips of pie crust are latticed across the top. This is a great pie...not overly sweet and very good with coffee or tea.
Thanks to the chowxperts for all the hand-holding.