1) How old are you? I will assume male.
2) You don't suck.
3) You are an aerobic king, that's why you can run a 10K just slightly slower than your 5k pace.
4) You need some practice running fast. For YOU I suggest some repeat 1000s. Goal pace. 90 seconds to 3 minutes rest depending on how many you do. If you get down the road a bit and you are finally running some faster 5,000s, then you can start doing some repeat 400s.