I don't know why would you want another card when you don't really needed it......you had 3 right now why wouldn't you used it and rotate it somehow.....no offense but if I were you I would call the bank you had $5000 limit and ask them why they won't show on my report. Ask them a limit increase if you haven't for the last 6 months........also credit increase on Sam and Crappy one too......used your SAMs card a ill bit once in awhile.........I think you might also call them to convert to their Discover Sam card........
3 credit line and 2 loan should be good enough for your credit score.....it's just grow slowly I guess........
Starting Score: 560