Misfire bad fuel milage told misfire 3 cyl

well 21 years old and no engine told at all, zero clues ,hard case that.
running 21 year old spark plugs and thermostat? and at 21 year old cam drive belt ? oops1,23,
oops.
what engine is it 1 or 3? we can not guess engines.
USA spec list , no country told.

1. 3.4 L 5VZ-FE V6 190 hp (2000-2004)yes
2. 4.0 L 1GR-FE V6 236 hp (2005-2006) NO and is CHAIN.
3. 4.7 L 2UZ-FE V8 yes and is interference n.

engine 1 and 3 are belt drive cams
the belt lasts for 60 to 90k miles, depends on belt maker quality.
if belt slips all cylinders drop compression HUGE and will misfire all
below 150psi per cyl. fails.
now the ASE macro list

1. engine bad. cam belt slipped.(sure it did ignored for ever)
2. bad spark, top cause 21 year old spark plugs and wire sets
3. weak fueling called lean misfire. injectors partly clogged or low fuel pressure FPR BAD this sold.

we do not know any cars service history here that be ESP wild.
and matters most (a fact)
21 year old parts love to fail.( a short list)
spark parts.(plugs and HV wires sets (no not mix up wires)
filters (both are tune up parts)spark filters
thermostat bad., not one lasted this long, eva.
battery main bad, (not this time)
alternator dead. cause battery *****.too.
bad fuel, parked for years idle.
bad belts, cam for sure most not be allowed to faill
bad cam belt on 4.7L bend head valves over. interference engine.

this is the short list.
scan of ECT and LTFT and 02 sensors
and scan PENDING DTC

If you had code P0305, I don't know why they would have done anything to the #2 cylinder but if they have already replaced the plugs, wires and injector; here are a few more items to check:
1) Check connections from ECM. Look for any corrosions or bent/broken pins.
2) Check the fuel line pressure
3) Check the engine compression
4) And if the above are good, then you will probably have a defective ECM

it means only, that combustion energy on cylinder 3 is weak.
it can be :
bad spark. #3
bad fuel ratio (lean or too rich) #3 (injectors)
bad compression. #3
we find it by doing tests, with simple tools

do you want guess or test?

Well you need spark at the right time, fuel, and compression.
I doubt you have a compression problem, so that leaves spark and fuel.
If the plug is firing, you could have a problem with the injector.

If it were low fuel pressure misfire , it wouldn't be cylinder specific misfire #2 , 4 it would be P0300 random misfire . I would think fuel injector's too . When hot they could be breaking down electrically , more resistance . If they tested electrically with a lab scope they would know for sure . Misfire from sticking fuel injector no fuel misfire

Spark plug wires will last 20 years in most cases
Spark plugs never fail to fire,they are replaced at 60,000 miles,
not over 3 years,regardless of milage.
Injector cleaner is useless and a waste of money.
How would 10 oz in a 15 gallon fuel tank fix anything
common sense.

Now you diagnose your drivability issue
Retrieve the code,if any, that set the check light,
proceed from there.

You stated a cylinder misfire,so you already know your problem
Coil pack, Coil -On-Plug,what ever you have on your vehicle.

The stalling is another issue,unless the misfire is so bad that it
spikes the computer,comes back on the TPS Sensor and the vehicle
goes into failsafe and shuts off. Still bad coil issues.

CODE P1300 IS MISFIRE DETECTED FUEL PROBLEM. WHICH MEAN 3 FUEL INJECTOR IS CLOGGED UP.HAVE FUEL INJECTORS CLEAN AND CHANGE FUEL FILTER.

please check on compression of all the cylinders. IF there is any valve damage this could cause a fault.Please check this out if your fuel and spark are ok.

bad fuel injectors or leaking intake.

Well you don't say what engine it has. I just had to put a helicoil in the head of a 3.4L 'cuz it had pulled the threads out of rocker arm bolt hole for cyl. #3. Car ran great afterward.