Hey guys, been a while since I've posted, but I need some help and hoping you guys might have some answers!

So I have a 2006 GT Convertible with 42,000 miles on it. I picked it up with 31,000 on it. Since day one it's had a rough suspension, and an issue where there is a "shutter" or "bumping" at all speeds and a SLIGHT shake in the steering wheel. Only suspension mods done is that it had lowering springs (not sure of the brand, but the last owner bought mostly brand name mods) and aftermarket wheels/tires.

Since then, I replaced and road-balanced all four wheels and tires with new. No help there.

Then upgraded the following:

Powerstop Street Warrior rotors and pads
FR GT500 Strut Mounts
FR Lower Front Control Arms
FR Wheel Hub Assys
Koni Shruts/Shocks
Moog Tie Rod Ends
SR Adjustable Swaybar End Links

Full alignment done at the shop I had the parts replaced at. She now runs tight as hell, rides a lot smoother, and absorbs bumps a lot better, however there was ZERO change in the shuttering.

Not commiserate with speed or RPM, feels the same all the time with the bumping, but the vibration starts getting really noticeable at 75-80.

Next step is to start upgrading the driveline (Clutch thru rear) which I need to do anyway, but want to actually troubleshoot before I go there, any ideas? Thanks guys!