Little bit of backstory, Its an Iroc with new shocks and struts, 90,xxx miles.

Any speed below 70-75 Feels fairly smooth, about how you would expect this kind of car to ride. Once i go past 75 it feels odd, I don't wanna say loose because i feel if i barely turn the wheel its going to veer off into tree or something. Is it normal for these cars to have such sensitive steering at that speed? Also, Its not a violent vibration but it does start to shake a little past 70

If this isn't how these cars should be, Any ideas what needs to be replaced to get it to feel solid and safe at higher speeds?

(Not sure if this is related, but somethings the rear end "clunks" going over speed bumps)

 

From the day it was new, my 83Z would start a vibe over 85....It was the steel driveshaft.

 

Tires will tend to do that. They will give a false sense of security above normal hwy speeds. Better quality tires will often negate that feeling.

What type of tires (brand and size)do you run and what tire pressure?

 

i will second the tires, i have a similar occurrence with a particular brand of tire on my 86 currently, but its closer to 90 mph