Wierd, I think it is the tires, but would like opinions.

It's smooth until 40 then vibrates from 40-50..... then smooth until 60..... then vibrates from 60-65...then smoothes out at 70 to 75, I have never been above 75 so I dunno after that. Lol

Everything seems tight underneath.

 

Could be tires, easy enough to check. Also could be a driveshaft. Check to see if balancing weights are missing on your tires and driveshaft.

 

Have your tires balanced and I bet it will go away.