Nefarious

Hey there everyone. I tried the search function and couldn't find anything on this. Sorry if it's a repeat. Anyways I have a 91 240sx SE Super Hicas with 170k KM on it. I have this slight issue with it. If I just really ease off and let it slowly climb to speed I notice it rev's up a little uneven. It will go up say 300ish rpm fine and then kinda slow down a bit in it's ascension, just for a split second and then go up another 300-400rpm smoothly. It's just berely what you could call jerky but it doesn't feel right. If I gun it it's not as noticeable. No white/black smoke out the car.

It has new NGK Platinum Plugs gapped to .044 (factory). When the car is warm and has been run for a while it isn't as noticeable as well. Generally it's when the car is still cold-ish and I drive off in the morning. I installed a new fuel filter (canadian tire).

Once I'm in second gear and on it's not really noticeable, just really in first gear. Also if I am in first gear and give it some gas and then let go of the pedal quickly it is a little jerky in decelleration and there is some 'bubbling' sound in the exhaust. Nothing loud, just a quiet gurgle sound? Any insight on this would be awsome. I was considering swapping for a better name brand/z32 fuel filter, maybe new plug wires?

Any help would be awsome guys(and gals)!!
Thanks,
Mike