Kind of tough to troubleshoot without data.  You've eliminated a couple of things except for the air leaks between the MAF and the throttle body or air leaks on the intake.  The reason I went there is because those things will make it run lean, and low fuel pressure would too. First let's check for codes:

To perform a KOER (Key On Engine Running) test, you need to ground the single wire at the EEC test connector (do you know where it is on that car?) and then start the engine (have the engine warmed up when you do this). 

After starting the engine with the single EEC test wire grounded, watch the Check Engine light and record the codes - the first code you get will be a 4 with nothing following it - that's a 40 and is normal for an 8 cylinder. 

When you get that code, tap the brake and jerk the steering wheel. The PCM will expect that because it can't check the Power Steering Pressure switch or the brake On Off switch without your help.

  The next code you get will be a 10, or a 1 with nothing after it. When you get the 10, very briefly slap the accelerator pedal to the floor, and then wait for the codes that come after that. They will be three digit codes, so count 'em that way.

Let me know what codes you get.

  In the mean time, since that car doesn't have datastream capability, you may need to tap into the O2 signal wire and measure the voltage - it that sensor is dead or intermittently flat lining, it can cause that kind of trouble, but since the spark plugs are lean (I assume you mean that they are very white?), you are more likely to have a fuel pressure problem or a MAF signal that is under reporting airflow. That can either be caused by a bad MAF sensor OR an air leak between the MAF and the engine.  O2 voltage should switch between zero and 1 volt fairly rapidly when monitored with a digital volt-ohmmeter - don't use a meter with a needle for this test.

Make sure there are no split hoses or air leaks in the plenum area or the hose between the MAF and the throttle body.

One thing you need to do is check fuel pressure - it should be 30 lbs idling and 40 lbs with the fuel pressure regulator disconnected.

 If it's running lean, that'll be an important piece of information.

That bogging down business sounds like O2 sensors coupled with a PCM that wants to run in closed loop but can't rely on what the O2s are telling it.  Problem is that usually causes one to run rich rather than lean.

If you have a in-range failure on your TP sensor it can cause crazy things to happen... it should read about 1.0 volt at idle and shouldn't be drifting around when you're not moving the throttle.  Also, it should go up smoothly as you smoothly move the pedal (engine off) to about 4.6 volts at Wide Open Throttle (WOT).

Richard

Manufacturer code 006 doesn't compute.. that's odd, not a code that's in the book... Sure that number's right?

Need to know what the fuel pressure is anyway...  When I'm doing one, I want to know what that is right after I check the codes.

NOTE:  I never heard from Ben Again... But gathering data and interpreting it accurately is very important for a successful repair.