My problem started at 70 mph like yours and gradually progressed to happening at 40 mph. I'm 90% through a front end suspension overhaul and found everything worn out. This includes Lower Control Arms, Tie rod ends, and Lower control arm bushings. All 4 of my shocks were also completely blown. So DIY budget should be around $1000 for everything I listed. $1500-2000 if you need to have a shop install it.