Hesitant Acceleration? Options

[Raeas]

I've been browsing the forums for quite some time but haven't yet pinpointed the exact problem.
Warm and cold, my car will idle fine, but occasionally the RPMs will drop and jump to normal a few times.
While driving, it will accelerate smoothly, but often it seems like it looses power and hesitates at any RPMs.
When it looses power, the car tends to buck and jerk or sometimes not accelerate at all.
If I increase the acceleration it still refuses to push and creates a pop from the excess air/fuel.
Last week it got to the point where it wouldn't drive a block without the engine dying
and it wouldn't even accelerate in neutral.

So far I've tried swapping plugs (NGK), changing oil and filter, changing the fuel filter, cleaning the buildup in the headers,
fixing any exhaust leaks, cleaning out the throttle body, cleaning the fuel injection system, changing the fuel pump,
and swapping old vacuum hoses (I made sure they matched the diagram) with new ones of the same size.

There was an oil leak from a bad seal that got into one of my plug's chamber which was fixed. Distributor and cap are fine. Air filter is clean.
All the maintenance that I did made it better and drivable, but it still does the same thing and I only expect it to become worse.
The car is all stock, no mods with a 5s-fe @210k. Bought it used not too long ago and it ran perfectly fine then.
I'm not really a mechanic, so anyone have any suggestions?

This post has been edited by Raeas: Mar 11, 2011 - 6:22 PM