Sometimes it doesn't happen for a while, other time especially if driving for a while and speed slowly increases and decreases and the RPM's are running somewhere between 1-2.5, the car very slighty jerks. It's an automatic so gets me worried.. Anyone experienced that?

not on my infiniti. but i noticed you have an infinity, so there might be something fishy going on... um, check for an intake leak. I had a friend experience 'jerking' at low rpms, cracked tube between MAS and throttle. also, run premium, knock and ignition timing can cause a little bit of jerking.

Easy way to check for leaks or cracks is to take a can of WD-40 and give little shots to area around gaskets, connection lines, fittings, etc. The engine will pick up the idle a bit if you hit the leak.

You may also want to check your injectors, fuel pressure regulator and fuel rail for the correct fuel pressure. If the car still runs strong upstairs, I actually doubt if this would be any problem, but there could be a chance that it would be masked by the higher rpm level.