I have had this problem for a while, Although it says cylinder 6 and 4 misfire now, Cylinder 3 also used to misfire Key word "used to" and that code no longer shows up however that was a while ago. Only recently have I checked it with an OB2 scanner again and now giving all these codes.

The Spark Plugs, Wires, and Distributer were changed a year ago to try and fix the misfire issue which from what I could tell did not fix the issue entirely or much at all. Since the codes says the engine is running Lean I figured I would change the Injectors since they were original from the factory and the engine has about 194k miles. This seams to not have helped much or at all.

Im guessing i should change the O2 Sensors? since that what the codes are pointing to and from what i know they have never been replaced, I have changed the PCV valve and some peopled told me about a Crank breather pipe that connects to the intake pipe before the throttle and to the left side valve cover and that it could be clogged? im also Skeptical of it being a Vacuum leak since i have already fixed one quite recently on this truck and it dose not seem to be a leak however I could be wrong.

Some other notes include: Sometimes the Engine would Vibrate somewhat Violently after idling (this would go away once you would drive away and give it gas) and may sometimes Stall or the engine would run a bit rough and then stall. MPG has gone down the drain but I know thats due to the Misfire. This issue has also been very sporadic, sometimes in the very recent past the engine would run totally fine and the check engine light would even go away, or at least the engine would run fine with the check engine light on but it would not flash signifying misfire.

 

First off, Lean codes do not mean the engine is running Lean, and Rich codes don't mean the engine is running Rich
These code mean the computer calculated fuel mix was lean so it added more fuel to the mix, which takes about 1/2 a second, so engine was running Lean for 1/2 second, yes its that fast at correcting fuel mix ratios
The Lean codes are set to notify the driver of the problem, but engine gets the extra fuel as needed

If engine is pinging/knocking it is actually running Lean
If there is grey smoke out the tail pipe then its actually running Rich

Yes, the P030X means a cylinder has misfired a few times in a row, has to be multiple misfires before code is set, and that's the vibration you feel

O2 sensors only see Oxygen, that's what the "O" is for, and Lean is high oxygen in the exhaust, Rich is low oxygen in the exhaust
When a cylinder misfires NO Oxygen is burned up with the gasoline, "no fire", so that oxygen is dumped into the exhaust pipes and O2 show Lean, high oxygen
So disregard the Lean codes until misfires are corrected

O2 sensors are the only sensors that have a mile or time limit, 100k miles or 12 years which ever comes first, they use a chemical to detect oxygen and that chemical gets used up
So yes, if your O2s are over 12 years old change them, or if over 100k miles change them, the misfires are not caused by the O2 sensors

So we need to deal with the misfires first
The first thing you should do when there is a misfire code is a compression test, to take compression off the table or find out it IS the problem, this saves time and money if it is a compression issue
Compression is a mechanical function, so good or bad, no grey area
Remove all 6 spark plugs
Test each cylinder and write down results, on a 3.0l above 150psi is expected, well on almost any engine, lol
But the point of the test is to get 6 numbers, in this case, a V6, and then compare them
Say you have 4 with 150 to 160psi, and 2 under 130psi, well there are your misfires, not a spark or fuel issue, compression issue
All 6 cylinders need to be within 10% of each other

To correct compression issue the heads have to come off and get a Valve Job, lower compression is 99% leaking exhaust valves

Doing new spark plugs or injectors is fine, but if its a compression issue these won't fix it, so best to find out first

P1121 Throttle Position Sensor Inconsistent with Mass Air Flow Sensor
That means you need to clean the MAF sensor most likely, easy to do

 

Thanks for the reply, I figured i would need to check compression which is somewhat making me a little worried
how much would a valve job usually go for?

also i mis typed p1121 its actually P1131

 

Rebuilt heads with new valves, and surfaced, run about $225 each, so $450, which can be cheaper than machine shop valve job, but call local shops to see
You do have to pay a Core Charge and send back your old heads, to get the core charge back

Head replacement gasket set with new head bolts runs about $130

I wouldn't be worried, it is what it is, you should look forward to finding out what's wrong, so you can fix the problem
If it is leaking valves then you will know, if its not you will know

 

When I pulled the heads off my '95 3.0L a few weeks ago I used Engine Tech gaskets from Rock Auto with new head bolts and it cost me around $80 with shipping. I had never used this brand before but after a bit of research, they seemed like an okay brand. They are a small company out of Texas that sources parts out of Brazil. Anyway, they seemed to work fine and the engine runs again. You might want to check them out to save a few bucks.