Why does my car feel sluggish?

Make sure your air cleaner is supplying enough air. I had the K&N 14x3 and it wouldn't supply enough air for my small block (meters 69gph of fuel when running at peak power) and it just starved at 5000rpm. I bought the K&N filter top and it made a world of difference in the performance. I imagine a 600 cfm carb may be a little small if you're running over 5000 rpm in addition to not having a large enough filter.