It has been six years since I last fished Lake Cushman. I use to fish it often. The key to limits was to find the Kokanee schools. That can be easier said than done on a lake the size of Cushman. I had good luck up closer to the Staircase end, and if the schools were there, you were in for easy limits due to the how shallow it is compared with to the SE end by the dam. There use to be a decent rainbow fishery as well, trolling along the shoreline drop offs was productive for rainbows. If you find the Kokes in the deeper middle, circle back in through doing figure 8s. When the schools move you have to re-locate again.
Sorry I do not have recent experience, and it sucks they are no longer stockings. But if I remember correctly Lake Cushman has a natural Kokanee run, and some natural CutThroat trout, so the stocking would be only for rainbows.