Missing. I have replaced plugs, wires, cleaned injectors, new injector, new fuel pump, cleaned fuel rail, new fuel filter, treatment 4 times in gas tank. What could this be?

Silverado 1500 or 2500 or 3500 or HD? no pickup told
not told the job you are doing>??
remove them all ,or scope them or just what, no job told
no end goal or task told. sorry can guess it.

like most V6/8 now , it is a sandwich.
the service manual covers all,l buy it rent it.?
toss dice and land on 1500
the rail on this engine, fuel rail like all , intake manifold injectors used;. all injector held down by both rails. left and right
now the steps to off them if is the job,
pull the isolator seen photo 1, far below.
1: pull left rail and right rail
Remove and discard the fuel injector retainer clips by installing EN-51097 injector retaining clip installer and spreading both sides of the clip evenly.
Always use NEW fuel injector collars supplied with injector when installing the new injector. If reinstalling the injector, it is not necessary to remove the collars unless the collars are being replaced.
Replace the injector seals as needed. Refer to Fuel Rail and Injectors Cleaning and Inspection.
Note
Inspect the injectors to be sure that they are clean and free of debris prior to installation. Do NOT lubricate the injector seals. Rebuild the fuel injectors whenever the injector has been removed from the fuel injector rail.


now I will past the other page rails off per the manual read to you.
just bank 1, i am to lazy to post both
step 1 rail off bank1.
Note
Inspect the injectors to be sure that they are clean and free of debris prior to installation. Do NOT lubricate the injector seals. Rebuild the fuel injectors whenever the injector has been removed from the fuel injector rail.

1. Remove the fuel pump insulator. Fuel Pump Insulator Replacement
2. Remove the fuel injector intermediate pipe position?1. Fuel Feed Intermediate Pipe Replacement - Position 1
3. Clean the cylinder head pocket around the injectors of any dirt or buildup.
4. Disconnect the electrical wiring harness connectors from the fuel rail.
5. the fuel rail fasteners are retained in the fuel rail by keepers and may be difficult to remove.Remove the fuel rail fasteners?(1) securing the injector rail?(2).
   Install two sets of EN-49248 remover?(3).
6. Install one remover in each of the fuel rail fastener bores.
7. Remove by turning each section of the EN-49248 remover an even amount to pull the fuel rail and injectors out evenly.
8. CAUTION
9. Remove the fuel rail assembly carefully in order to prevent damage to the injector electrical connector terminals and the injector spray tips. Support the fuel rail after the fuel rail is removed in order to avoid damaging the fuel rail components.
10. Cap the fittings and plug the holes when servicing the fuel system in order to prevent dirt and other contaminants from entering open pipes and passages.
11. 1. Simultaneously lift both ends of the fuel rail?(2) and remove the fuel rail assembly from the cylinder head.
12. Remove and DISCARD the fuel injector seals.
13. Some vehicles were not originally equipped with fuel injector dust seals. A NEW seal must be installed when the injectors are removed.
    Remove and DISCARD the fuel injector dust seal (1).
14. NOTE
    Note
    Whenever the fuel injectors are removed from the cylinder head or fuel rail, they will need to be rebuilt. Fuel Rail and Injectors Cleaning and Inspection
    If replacing the fuel injection fuel rail, remove the fuel injectors. Fuel Injector Replacement

Installation Procedure, skipped me. the service manual lists 4 tools
per

Special Tools

1. EN-49248 Injector Rail Assembly Remover
2. EN-51105-1 Injector Seal Installer and Sizer
3. EN-49245-3 Fuel Injection Seal Installer Sizer
4. EN-49245-4 Fuel Injection Seal Installer Sizer

this is first. pull the isolator.

this one step is the GET TO ANSWEREd
Injector work 10x more complex and special tools needed x4

so missfire detected and cylinder 3 missfire detected.
check to see injector pulse with "noide light" if ok injector is problem
remove fuel rail and injectors look into top of injector for blockage in screen filter in injector if blocked clean out or injector carby places can remove this screen replace it and test injectors and clean or just buy new injectors. make sure to clean out fuel rail and change fuel filter also.
if noide light flashes irratic or not at all wiring issue, check for power on one wire with ignition on 12v other is earthed by ecu when opened to inject fuel. other thing that can cause problem on cylinder is tappet clearance "shims" too tight, could do compression test to see if compression is low on cylinder or a cylinder leakage test to see if valves are leaking. broken valve spring. valves do not hit piston on these engines even if cam belt breaks, they are a "free wheeling" engine

White smoke from the exhaust is usually an
indication of coolant in the cylinders, from a
possible bad head gasket or other gaskets

May be time to parts with it, when you find
out the repair cost

WELL I WAS GOING TO SAY REPLACE FUEL FILTER, CLEAN FUEL INJECTORS BY ADDING A CAN SEAFOAM TO 3/4 TO FULL TANK OF GAS.REPLACE SPARK PLUGS AND WIRES. DO A LITTLE TUNE UP SEE IF HELP COLD START CONDITIONS. IF CAR STILL TAKES A LONG TIME TO CRANK. FUEL PUMP FAILING THE CHECK VALVE IN FUEL PUMP IS ALLOWING ALL FUEL LEAK BACK IN THE FUEL TANK.

If one cylinder is missing at idle, it would be useful to know which one. Pulling the plug wires one at a time with insulated pliers would tell us if one does not cause a change.
It could be a fouled plug.
You could switch plugs with another, to verify.

If not spark, could be fuel.
If throttle body, then not likely.
If individual injectors, then pull whole rail off and see if all injectors fire, spray pattern like cone, and none dribbling.

If none of above, then consider intake leak, collapsed lifter, valve adj, etc.

Replace fuel filter, because it is cheap & easy, and may solve problem.$20
Fuel injector cleaner in the gas tank $5...listen for even ticking sound in injectors at idle and higher RPM. Injectors can be services/or replaced easily. $60 each
Fuel pressure regulator, next to fuel rail, may be going out...$75
If you have an in-line pressure guage, you can meause the fuel pressure to see if is within specs.

take line off before filter see if gas is coming out at time of key engagement, if not its fuel pump.if yes then reconect and disconnect on outlet side of fuel filter this will tell you if filter is clogged

Best do a fuel pressure test. Should have chg. fuel filter from the get go. The only other filter is on the end of the fuel pump in tank. Bad gas and dirty gas will plug up fuel filter, hense burn pump up.

An injector can pulse without spraying fuel. They can get plugged or get build up on the nozzle and squirt fuel instead of spraying or not spray at all.. Your fuel rail is common rail, so your fuel line should go through a pressure regulator and then to a rail that dispenses the fuel equally. I have heard of cases where kia replaced the fuel rail to solve this problem. All the injectors will get the same amount of fuel pressure with this system, so if you have injector pulse and no missfires on #2 and #4, i would suspect clogged injectors. You can have an injector flush performed, which is probably not a bad ideal any way, to see if you can clean them up, or just replace the bad injectors. You can also inspect them visually to see if there is any debris on the nozzles. I wouldn't recomend that to an inexperienced person. Fuel can be very dangerous. I have head of techs removing the injector from the rail and running the car and watching the injector spray the fuel. Not recommended at all. All it takes is one spark or hot surface. Do a fuel injection clean, or buy some BG brand 44k fuel treatment and put in the tank first, the fill it up with gas. You can remove the injector and soak it in injector cleaner also to help free it up. If any of these don't help, time to take it in...they are also experiencing ECU problems..

on the bad gas part I would recommend to get some STP gas treatment with injector cleaner to put into the gas tank
try a salvage yard that has a 302 engine like yours and change the whole distributor because the shaft could be bad on that end