BACKSTORY
This truck has been sitting in the driveway for 2+ years. The miles are really low, only at 40,000K but before getting towed to the driveway as a temporary grave site it had starting issues. I always suspected the fuel pump, but never got around to confirming that. Last week I replaced the fuel pump and found two deteriorated hoses, a disintegrated fuel filter on the bottom of the tank, and sediment. I pumped out all the old fuel (the tank was freakin full by the way), cleaned the tank, added the new fuel pump, primed the line and to my surprise the engine fired up.

DIAGNOSING
Ok, well the truck fired up but it sounded angry and the body was shaking vigorously. Maybe there's some bad gas in the lines some where? After letting it idle, i remembered I had a obd scanner and popped it in to see some data. The shaking decreased but it still shakes more than I remember (which is 17 years ago). Codes P0171 and P0174 were pending for a bit until they were finally thrown. I've come to terms that there is likely more than 1 bad component.

FUEL
My fuel gauge sits at 66 PSI and doesn't move when I rev the engine. But i'm not sure I can rule out fuel just yet. Can you have a bad fuel filter and good PSI? Changing the fuel filter is my next step for this weekend, and then investigating the fuel injectors. I'm assuming this is all the fuel related components to check.


AIR/Vacuum
I cleaned out the throttle body and the IAC Valve, the best I could. After doing the IAC unplugging trick my 750rpms dropped to 630 rpms. Not quite 500rpm so I haven't ruled out any leaks. After spraying my entire can of carb cleaner, I haven't found a Vacuum but there's gotta be one. I think.

Here's my graph from idle to 2000 RPM's. You can see long term trims lowering for 1 and 2, but also short terms increasing?

my MAF was showing 10g/s here but it's been between 4.0 to 5.0 at idle.

Should I be rushing to build a smoke machine and 100% rule out leaks?

Thanks for your input.

From idle to 2k rpm's

 

Yes fuel pressure is fine now, 55-65psi is spec

Your Long term fuel trims(LTFT) are setting the codes, +20

They were that high BEFORE you even started the truck after 2 years, computer doesn't forget LTFT, thats the point of LTFT so computer doesn't have to re-learn air/fuel mix every time it starts up
If fuel pump was failing that would explain higher LTFT

I would put a can of Seafoam, or similar injector cleaner, in the gas tank, that will help clean up injector tips, and go for a few longer drives if possible, at least 45min on the highway

MAF sensor should be cleaned once a year, rule of thumb is MAF will read displacement in g/s at 500RPMs, many miss that 500rpm part, so if your 3 liter engine is idling at 750rpms then 3.8-4.2 g/s wouldn't be out of line

If RPMs dropped when you unplugged IAC Valve(warm engine) then no vacuum leaks, at least none large enough to explain the high LTFT

You could replace the 3 O2 sensors I am sure they are running out of chemicals after 17 years, it wouldn't hurt, they are normally replaced after 100k miles or so, which is 8 to 10 years on most vehicles

What you need to see is STFT in the negative so -2 to -5 STFT that will bring down the LTFT after a few weeks

LTFT is "like" an average of STFT not quite but "like", and the rear O2(O2 2x1) also plays a part in that, it should be at .7 or .8 volts but will drop and then go back up, thats normal

O2s can only see Oxygen, O2s generate their own voltage using a chemical reaction with oxygen, .1v is Lean(high oxygen), .9v is Rich(low oxygen)
O2s can not work under 650degF, so computer ignores them until exhaust heats them up, 3 to 5 min from cold start, they also have internal heaters so they heat up faster
The 2 front O2s change very fast but should average .3v to .5v

The rear O2(downstream) sensor is after the Cats, the Cat converters burn up most of the oxygen trying to clean the exhaust, so O2 shows .7/.8volts, low oxygen, not "rich" in this case, just less oxygen left
It will drop down and then back up as the computer feeds a rich fuel mix thru the engine every few seconds to give the Cats some unburned gasoline to keep them HOT and cleaning the exhaust

 

Tiny update. I added fuel injector cleaner (STP brand) to a full tank of fuel and drove around the neighborhood and back roads for about 20 minutes. I did mostly slow speeds, and the top speed I reached was 45 mph but didn't really get on it until the end of the drive. Meaning 0 to 45mph, 1st gear ~4,000 RPM shift quickly, to 2nd maybe 3500rpm and got my way up to 40. How did it feel? Part of it felt like old times, that it wasn't sluggish and I should just take it to the highway but I was already on my way home. Plus I wasn't ready for that confidence wise, since most of the drive it was clearly lackluster in power. The shifter wobbles and shakes so much starting from a stop and sound like i'm trying to start in 2nd gear even though i'm in 1st sometimes.

I don't recall when these codes were fired, but my scanner found some "pending faults". While driving, before the 'harder' acceleration to 45mph, the check engine light came on, then turned off. Sometimes it would flash, then go away. So the new issues: i'll check if they are reoccurring this weekend are codes p0300, p0303, p0306, p0316 .

My new O2 sensors came in the mail today. Bosch 15716, and 15664. I'll get them in hopefully tomorrow if there's no rain and maniac ants on the ground and put some miles in to burn off the fuel injector cleaner.

 

Well P0303 and 306 means rear cylinders on both side of the engine are misfiring
I would pull the spark plugs and have a look at the tips, see if they have a blackish color(oil) instead of a very light brown(good burns)

Also when you can, test fuel pressure, you can often get a testing gauge free(loan) at autoparts stores, or rent a gauge kit, they are only $30 new, often $10 to rent
If you can take fuel pressure off the table then finding the cause for Lean on both banks would be easier
Fuel pressure is a good or bad test, there is no grey(maybe) area, 2003 needs to have 55-60psi