Hi. My name is Luis and I'm the owner of a C4 Coupe LT1 1992. There is a situation with the car and need to know what could be happening with it. The Corvette drive very smooth at any speed with the roof top on, but without it the drive become very unstable or unsteady.
I recently purchased a 94 c4 and I felt a lot of interior buffiting. Air caught at the back window. More air flow than the rear vents can handle. I went to Corvette america and bought a rear hatch vent latch. You bolt it to the rear window latch and it locks into the body. This will let the air flow out the back and silence the buffiting and smoothen out the ride because cross winds won't affect the interior. I use mine all the time and it works great for me. It may help you.