Welcome to iRV2.
Could you add some info to your post .
Chassis manufacturer ? Size of tires ? Bounce ( vibration) apparent at all speeds and in every transmission gear? Same under power, cruising and coasting ?
Were the tires , spin balanced ? Rims checked for excessive run out before the new tires were installed ?
There is a distinct , difference in the speed of a drive shaft vibration , and that produced from tires and wheels ; drive shaft is turning over 4 times as fast.
Has a mechanic ridden with you to determine if , it's a slow or fast vibration ( bounce )?