71 Duster Dyno

[ame="https://youtu.be/iu447kSmPGE"]https://youtu.be/iu447kSmPGE[/ame]Finally had a chance to take it to the track, was super nervous for a first timer but had a blast. I ran with street tyres and a very conservative launch spun through 1st and most of 2nd once it hooked up it went really well but could never hold 4th flat past 150kmh because it was swaying violently. Ive attached a vid for your reference any advice on why its swaying so much would be appreciated.

Ran a 13.4 @ 109mph