I never noticed the fishing being that bad below the dam. Grew up in Grayson county, fished there mostly in the early 90's as a teenager. Not sure how the stripers could have ruined the river but not the lake. Texoma is a really good catfishing lake too.
This^^
Fish the holes below the dam about an hour after they shut down the generators. The channels will be there. I have a friend that fishes there all the time and he throws a big fish fry party several times a year after 2 or 3 nights of fishing. I've been with him a couple times over the years and it easy fishing. If they haven't run the generators for a few days, just move downriver and fish behind every obstruction you see.