99 jimmy no power

My truck over the course of 3 days of driving and 4 days of sitting and me checking parts is to the point of not making it around the block.
It all started with a little more fuel peddle to get it going, to 3000rpm to hold 80 kmh on a mild grade and starting to chug. So now sitting in the driveway in park I can't get it to rev past 3000 and if i hold at 3000 the revs drop off to 2200-2500 and slowly pick up again.The truck seems to heat up fast and does run better for the few minutes it's cold.
Okay things I've done so far
fuel presure test 62 psi not running no leak down 60-61 psi when running.
cleaned maf and throttlebody
cleaned egr
changed fuel filtre
checked coil it was good but changed anyway thought it might be failing when hot
vaccum test 18psi when running hit it to 2500rpm and let of peaks 23 drops to 8-10 and back to 18
changed rotor and cap old ones looked good only 20k on them
checked 2 plugs looked like new and put them back in
checked the cat 100f between the front and back at idle 350f after reving at 2500 for a minute
so far I've got three codes po300 po101 po102
I still want to check temp sensor but i can't seem to find it, also I found a pressure sensor behind and to the left(if facing the motor) of the throat of the throttle body curious as to what it is.
Any help would be greatly appreciated

Fuel pressure is low.
You need to run afull fuel pressure check.

Code 101 and 102 are MAF sensor codes.
Unplug MAF sensor and see if it runs better.

Clear codes and see what comes back.

The only true test on a fuel pump is to check the direct fuel pressure from fuel pump.
A quick test is to block off the return line and see if fuel pressure comes up to 75-85 lbs.
But do not run the pump at full pressure very long.
Also when testing fuel pump and pressure you need to tape a gauge to outside windshield or outside mirror and drive it on the road for 20 -30 minutes
until the pump gets has run a while to check for a pump fading out after hot.

Hard to start cold or hot and fuel pressure testing guide lines.
Check cold start fuel pressure.
Check engine running fuel pressure.
Check engine running on the road fuel pressure.
Then shut it off and watch for fast leak down.
Pinch off at rubber part or block off return line and check full pressure.
If pump has full pressure with return line blocked and low pressure without it blocked most usually the fuel pressure regulator is leaking or not holding pressure.
Later V6 and V8 gm engines should have 60-66 fuel pressure.
Cold start should be 64-65 lbs of pressure.
If you do not have full fuel pressure on a cold start the injectors will not squirt fuel.
Do not leave home without it.
Engine running should be 60-66 lbs pressure depending on engine load.
Full pressure with return pinched off should be 75-85 or more.
And if it has a fast leak down after shut off you have a leak in system.
Post back fuel pressure readings.

And let us know what codes come back and how it does with MAF unplugged.

unplugging the maf does not change anything and sets a po102 code

fuel pressure on a 10 min tour never went below 60 psi and there is no leak down when the engine is off

You need to be seeing 65 lbs pressure cold cranking start.
And 64-65 on the road under load.
Run the full test on the fuel pump.
And post back results.
MT

Always diagnose DTC's in the order they appear on the scan tool. Whatever is causing the P0300 could very well be causing the MAF sensor DTC's to show up. If the P0300 is first, the most common cause is secondary ignition: Distributor cap, distributor rotor, plug wires, plugs, and ignition coil. A/C Delco parts will provide the best performance. Aftermarket parts are a "crap shoot", especially when it comes to plugs, cap and rotor.

Mt I'm afraid to drive the truck that long with the way its running

So today I took of work to try and get this truck running, took the wife to work so I'd have a vehicle to get parts if I needed.
MY cat temps got me thinking the 350 f difference between the front and back of the cat particularly. So I checked the wifes car at idle and after running down the road only 70 -100 f between the front and back.
So i pulled the o2 sensors before and after cat took the truck for a drive and it's got all it's power back, put the sensor between the cat & engine back in but unplugged the truck started running like a piece of shit again, pulled the sensor again and the truck was running great.
Looks like it's time for a new cat and a couple of new o2 sensors since I have them out

If the cat is plugged you also need to fix the problem that made it stop up.
Or it will plug up again.
Go over tune up and engine running real close.
Rich exhaust or missfire is the leading cause of cat problems.
MT

I agree, a restricted converter is a result of the real problem, it is NOT the cause of the problem. Your SES light is telling you the cause, P0300, random cylinder misfire.