Shaky Front End on Cadillac Deville DTS

I have a very bad shaking in the front end of my Cadillac (2004 - 60,000 miles). I’ve replaced the tires, aligned the front end, and now replaced a wheel bearing (which eliminated a roaring sound as I went around right hand curves). Unfortunately, the shake is still there. Mostly between 60 and 75, worse when I slow down from that speed (both with and without braking), and seems to cycle through bad shakes and not so bad shakes every 30 seconds or so. Any ideas?