2010 2.5X MT Rear End Play (a lot)

I have been trying to tackle this issue with my wife's car and I can't figure it out. I have brought it to 3 mechanics, all of them saying there is no issue, but I know there is an issue. I have had people in the car that have felt the problem, but its hard to describe the issue, because it doesn't happen on every bump, it usually only happens at about 40+ mph, and it doesn't make any noise. Also, my tires seem to be wearing a little to quickly, The tires have less than 20,000 miles on them and they look to be worn a lot.

A little backstory, over the winter, during a storm, I hit a rather large branch in the road that busted up the grill, the passenger headlight and dented the hood. I replaced all of that stuff myself. I noticed that the alignment was pretty off, so I got the car realigned and I put my summer tires back on a few months later.

I started noticing the issue, and reading around (even made another post about it), and it seemed like maybe the issue was my front struts, so I replaced the full assembly on both sides, and still have the issue. I then started checking sway bars, bushings, endlinks, tie rod ends, rear struts...it seems like everything is fine.

I have the car at a mechanic now, they said it seems fine, the car is aligned, the tow is good, but again, I know there is a problem, I know these are floaty and boaty, but this is much more floaty and boaty than it should be. The back end seems be slipping out when it hits a sequence of bumps, and rather violently at that. I have had the traction control light come on after hitting some of those bumps that knock the back end out as well. The mechanic is going to check the sub frame bolts for me as that's something else I have read, but I didn't know if there was a drive train issue as the tires are wearing a little quicker than they should.

I'm pretty handy, so I can probably take a look at anything anyone recommends (hopefully). My wife is almost 40 weeks pregnant, and I have told her that I am not really comfortable with her driving in that car, so i'm trying my hardest to get it fixed.

Any help is appreciated, and if you need any additional info please let me know.