Why do RPM/engine surge when over 80mph?

I have a 2016 Nissan Sentra. It only has 65k miles on it. When I hit 80 mph, the rpm needle starts jumping up and down by 20 rpms back and forth, as the engine revs. The car when physically lurches a bit.

Also, maybe unrelated, the AC is only cold when I'm driving at least 60. The AC also “revs” and blows sporadically at different speeds on its own.

Please give me possible causes. If like to have some insight before I go to the autoshop and get lied to left and right.