Engine hesitation and stuttering progressively getting worse.

To begin, this car is a 2000 Saturn LW2, not a L200. The website did not allow me to choose LW2. It is the 3.0 V6 model. I presently have 195,000 miles. Over the last 30,000 miles or so, the engine has been hesitating/sputtering a little bit at low rpms (probably 1,000-2,000 rpm range). Over time, this has been getting worse. The hesitation/sputtering feels as if my foot was very unsteady on the gas pedal, even when holding it completely steady. The engine will sometimes feel like it is struggling, then surge sometimes. Just very unsteady. When this happens, you can see the tachometer go up and down accordingly. This does NOT happen when switching gears, but while in gear. In order to narrow it down, I tested it in Neutral with the E-brake on, and the hesitation/sputtering does happen. If you do not press the gas, the car idles perfectly at about 700-800 RPMS. However, the hesitation only happens when you lightly press the gas.

Here is a list of things I have tried over the last year or so:
1. Replaced the spark plugs
2. Replaced the front and rear ignition coils
3. Used high quality fuel-injection cleaner
4. Replaced air filter
5. Replaced Fuel Filter
6. Cleaned the MAF sensor
7. The fuel pump is only about 12-18 months old (though I'm not sure if the problem was before or after the new fuel pump.

For the most part, I have not had any check engine lights. I had some a few months ago, but they were due to a failing ignition coil. Last week, I got the check engine light, and after getting a free scan at the parts store, it revealed a whole slew of error codes:
p1811 - Maximum adapt and long shift
p0402 - Excessive EGR Flow
p0405 - EGR Position Sensor Low Voltage
p0171 - Fuel System Too Lean (Bank 1)
p0174 - Fuel System Too Lean (Bank 2)
p0051 - H02S Heater Control Circuit Low Bank 2 Sensor 1
p0152 - Oxygen Sensor Circuit High Voltage (Bank 2, Sensor 1)
p0300 - Cylinder Misfire Detected – Random Cylinders
p0303 - Cylinder #3 Misfire Detected

After receiving these codes, I have replaced the rear ignition coil, the air filter, and cleaned the MAF sensor. After doing this, the check engine light went off. I think this may have resolved the P0300 and P0303 because the front ignition coil failed not long ago. However, yesterday, the check engine light came back on. This time, the ODB scanner only revealed 1 error code. This code was a P0050 (H02S Heater Control Circuit Bank 2 Sensor 1). After doing a little research, we thought it may have been a faulty Oxygen sensor. I believe this car has 2-3 sensors, so I tried to determine which one I thought may be the problem. After a little research, I believe the bank 2 sensor 1 was the oxygen sensor near the front of the engine (cylinders 2, 4, 6) near the exhaust manifold. We replaced that today, but the problem persists. The car drives fine at highways speeds. In fact, sometimes the car accelerates smoothly. The problem seems to come and go quite regularly.

I have tried to be very thorough in explaining the problem. Please let me know if you can help. I am hoping to fix the problem myself without spending too much money, if possible. Thank you!