Jason
I pulled up a map of your lake from the web and man what a lake. It's over three times as big as Patoka Lake. I noticed it had many creeks running into it from the dam to the upper end. I would start in the upper end of the lake before the water hits 55. It's much smaller and I'd say easier to fish. Those crappie usually visit and stay in the same areas as spring until cold water temperatures make them move out deeper. If you've got shad in that lake look for balls of them on your depthfinder as you motor into the creeks. They usually show up as one huge mass on mine. I don't fish standing timber much either cause everyone else usually beats the hell out of it. I like channels and deep humps with cover on them period. If you do not have well defined channels look at the surrounding country side and look at those gullies where the water drains off. Picture this in your mind as you motor into an area of what it might look like under water. I also like isolated stumps with nothing around them. My biggest crappie a 2.6 lb came off of a single stump in 26' of water. Seen the fish on my trolling motor depth finder and caught it less than a minute later. You said your catching several fish off your cover but no more, try finding cover at those depths in the upper end and I'll bet you'll find schools of crappie. As it gets colder work your way down towards the lower end. A lake that deep will take a long time to cool off. It took me many years of slow poking around my lake for me to find the cover I've found. I'd take my wife and kids out on the pontoon boat riding around. My Lowrance X-15 I had on that boat was on all the time. I kept them happy and learned alot about the lake in the meantime. When I bought the maps I have of the lake I put that information on them. Now after fishing this lake for 26 years I got a pretty good idea where they should be at almost anytime of the year. The areas I fish I've fish so many times I can visulize in my mind the cover I'm fishing. I know the high spots and low spots. It's a picture on the depth finder going through my mind. And every now and then make a fool out of me. It's the days when you whip their butt real good that makes it all worthwhile. I'd like to fish your lake along with many others in this country but don't have the time and all the money it would take.
The guys that fish for a living probably will give you a better answer than mine. They're on the water alot more than me. What I decribed works for me.
Good luck and good fishing.
Larry