FLA370Z

So I have searched around the forums and couldn't find anything similar to my situation. From around 75 to 90 mph I get this shake/vibration starting from the rear and like a wave moving towards the front....the weird part is that it will vibrate for 10 seconds then go away then come back for another 10 seconds at the above mentioned mph range continuously cycling. I was looking to see if anyone has gone through a similar experience and what their solution was. I will list potential problem areas that I have eliminated below do to recent service and checking:

1) I have aftermarket wheels and Michelin PSS tires (75%), all wheels were just high speed balanced and have the proper hubcentric rings on hubcentric spacers.

2) I have after market Stillen Sway Bars front and rear and all new SPL endlinks.

3) Checked the driveshaft U Bolt and seems to be fine

4) I don't know if this matters but I just changed the transmission fluid and diff fluid with the recommended Red Line products.

5) I'm on HR springs with adjustable camber arms, vehicle is fully aligned.

6) I have taken the lugs on and off a handful of times, properly torquing them down each time.

This issue started about 2 weeks ago and nothing has changed from a aftermarket part standpoint. My setup above has been like that with no issues running those tires and wheels and spacers etc.

The only thing that has been recently changed is the diff (75W90...2 Qts) and transmission (MT-85...3 Qts) fluid change but that went smoothly and I believe is unrelated but figured I would put all information down.

Any help/suggestions would be greatly appreciated, thank you.

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Stillen Gen 3 Intakes | Berk Test Pipes | FI 12''| Eibach Front & Rear Sway Bars | HR Springs | SPL Front/Rear Arms | ECUtek | Akebono BBK