Congratulations Rhino. Seams in fast section of the river can be quite good for coho salmon as you have discovered. Fish travel up the fast water and sit in these slower slots briefly to rest. This opens up opportunities for them to bite. The takes are usually quite fast because of the short reaction time and fast current, therefore it can be quite exciting. Sometimes you can work your way down the river with no success, only to come back and find fish in slots that have been fished because they are always on the move.
The gear adjustments needed for the faster current are heavier weight to get the presentation to the depth quickly and shorter leader so the presentation stays in the strike zone. Heavier line may also be advantageous if the amount of fighting space is limited.
I personally dislike fishing this type of water, not because it has not been productive for me, but I simply have a bigger preference on fishing moderate flows where you can spend more time at each location. It can also be frustrating at times if roe constantly falls off the hook due to the current. The alternative presentations would be wool, plastic bait and roe bags.
Good luck.