rear shocks

Hello all. I am new to the forum so if this is a common thread that I can look at somewhere, please direct me. I have a 2013 Maxima SV without the sport suspension. When I hit expansion joints or bumps, the rear of the car jumps sideways. It also clunks. I have had it to the dealer as well...

I apologize as I don't know all the terminology of parts here. I have attached a photo. Basically, I was trying to loosen that single bolt that holds the rear shock to the boot/mount. It did not want to budge..so I used some penetration grease and let it sit overnight. However....same...