2006 altima skipping gears

[06altima3.5]

Hi guys first of all Im new here, i happen to stumble upon this website on Google and found it very helpful, well my question is, i have a 2006 Nissan Altima 3.5se and lately its been skipping gears. i just be driving down the road at a slow speed and as Im driving the transmission would just skip a gear, it just jumps to neutral out of no where and all of the sudden jumps back in to gear. i took it to get the transmission look at and they said it was fine. the car does not have a code on the dash i took it to auto zone but they couldn't help me. Does anyone have any idea what it could be??