That's just the inherit nature of slicks is that they give you an uneasy feeling on the top end to differing degrees, that is why the radial classes are so popular now as they are way more stable feeling at speed with the increased sidewall and ultimately faster than a slick. The main advantage of a slick over a drag radial in my opinion is the fact that a slick can recover from a slip of the tire and infact a controlled spin is actually wanted to obtain wheel speed for a slick to be fast whereas a drag radial does not recover well if you knock the tire off.
