As a follow up, Here's some additional info on my problem...
I notice that when the car is cold I don't have the problem. But as the car warms up after a few miles of driving, the RPMs at which I am able to run the car successful (without hesitation and jerking) decreases until it reaches about 2000 which then becomes the threshold. It's like the engine is choking and the muffler also seems to be coughing a bit.
I do have the typical exhaust manifold problem but never had the repair done as I was told it would not affect my pathfinder's performance enough to be worth it. I'm not sure if this now is a contributor of this latest problem.
Someone suggested I replace the fuel filter and spark plugs which I did, but didn't solve the problem, so I'm still seeking a solution if there is anyone that may know.
I will probably have it professional checked out.