2000 navigator won't shift into park

First decide which cylinder is misfiring and see if the sparkplug has been damaged. Check cylinder compression. All should be about equal.

Oil pressure sensor or switch has to be connected to the main oil gallery and it is generally most convenient screwed into the oil filter head or the gallery side of the cylinder block - you omitted to say whether your car has an oil pressure gauge?
If there is a gauge the light might be switched by the gauge itself or if the gauge is electronic and computer driven, the computer might be switching on the light.

It is worth checking the vehicle handbook or a wiring diagram to be certain what you have and how it works.
Some vehicles are no longer fitted with an oil pressure light and other vehicles have a light for the oil pressure and another for temperature and/or oil filter blockage.

Low oil pressure light on shouldn't be taken lightly and if a replacement switch/sender doesn't cure it, you should have an oil pressure test carried out asap.

If your oil pressure gauge is reading normal I wouldn't think so. You need to get your codes read with a scan tool and find out what the computer thinks the problem is.

Did you fix the trouble Codes? Both are fuel related. There is a test done with a special machine called a "Smoke test". This could also find out if there are holes in your fuel tank and where.

The failure of your system to maintain Vacuum pressure is a good indication the fuel system has an opening.

see this tips and fix it. God bless you
The oil pump supplies oil to lubricate your engine. If the oil pump is worn or is not turning, the engine will suffer a loss of oil pressure, which may result in engine damage or engine failure.
The first sign of trouble may be a low oil pressure warning light, a drop in the normal reading on you oil pressure gauge (if your car has one), or the appearance of ticking or clattering sounds from your engine.
As a rule, most engines only need about 10 PSI of oil pressure for every 1,000 RPM of engine speed. Oil pressure will read higher than normal when a cold engine is first started because the oil is thick. Oil pressure will gradually drop as the engine warms up and the oil thins out. So normal oil pressure on a warm engine cruising down the highway is typically 30 PSI up to 45 PSI.
SYMPTOMS OF OIL PUMP TROUBLE
The first thing you should do if any of these symptoms occur is to stop your car, turn off the engine, let it sit for a few minutes, then check the oil level on the dipstick. If the oil level is at or below the ADD line, add a quart of oil to bring the level back up to the full mark. Add as much oil as is needed to raise the level to the full mark. Then restart the engine. If the warning light remains on, or the oil pressure reading does not climb back up to its normal range, or the engine noise does not go away, you may have a bad oil pump.
The other possibilities include a bad oil pressure sending unit, or a problem with the oil pressure warning light circuit or oil pressure gauge.
OIL PRESSURE SENDING UNIT
If the engine is NOT making any unusual noises and seems to be running normally, and the oil level on the dipstick is FULL, but you are still getting a low oil pressure warning light or low gauge reading, the fault could be a bad oil pressure sending unit.
The oil pressure sending unit is mounted on the engine block. On some applications, there is a spring-loaded pressure-sensitive diaphragm with a switch inside the sending unit. This switch completes the circuit to the low oil pressure warning light if oil pressure drops below a certain threshold. The unit may stop working if the diaphragm inside fails, if the switch is stuck, if the small hole that allows oil to enter the sending unit becomes plugged, if there is a loose, corroded or broken wiring connector at the sending unit, or there is a fault in the wiring circuit between the sending unit and warming light.
On vehicles that have an oil pressure gauge (electronic, not mechanical), the oil pressure sending unit has a small rheostat inside that sends a variable voltage signal to the oil pressure gauge when the diaphragm moves. A worn spot on the rheostat or any of the other problems just described for the simple pressure-type oil pressure switches can cause a problem.
FORD'S FAKE OIL PRESSURE GAUGE
On many Ford vehicles that were built from 1980 through the 1990s, the oil pressure sending unit has two switches, a low pressure and a high pressure. These vehicles also have an oil pressure gauge, but the reading on the gauge is not a true indication of real oil pressure. As long as the pressure to the sending unit is between high and low, the gauge will read normal. If oil pressure drops and trips the low pressure switch, the dash gauge will now read low. Or, if oil pressure goes up and trips the high switch inside the sending unit, the dash gauge will read high. Consequently, don't rely on the oil pressure gauge for an accurate reading in these vehicles. It is only a gross indication if the oil pressure is low, normal or high.
OIL GAUGE PROBLEMS
If the engine is NOT making any unusual noises and seems to be running normally, the oil level on the dipstick is FULL, and you have replaced the oil pressure sending unit but are still getting a low oil pressure reading on the dash gauge, the fault could be in the wiring circuit between the sending unit and gauge, or the gauge itself might be bad.
Check the wiring connections on both ends as well as wiring continuity between the sending unit and gauge. If no wiring faults are found, hook up a pressure gauge directly to the oil pressure port on the engine and check oil pressure with the engine running. If the engine-mounted gauge shows normal oil pressure but the dash gauge is reading low, the problem is a bad dash gauge.
On the other hand, if the engine-mounted pressure gauge reads low and you have done all of the above, chances are the oil pump is worn, or it is not picking up enough oil because of a restriction or blockage in the pickup screen in the bottom of the crankcase.
OIL PUMP PICKUP PROBLEMS
The pickup tube has a screen on the end to prevent large chunks of anything bad that ends up in the crankcase from being sucked into the pump. But we are talking BIG chunks of debris, not normal wear particles or carbon or dust or other microscopic-sized abrasive particles that can cause pump wear over time.

Normally you clear the codes with a scanner or code reader. You could disconnect the battery and see what happens, but I doubt trying to reset it will help.
Sounds more like a wiring problem or something inside the computer.

With an oil pressure gauge:
Remove the oil sender unit and install an oil pressure gauge at the cold engine and let the engine warming up. And record oil pressure data.
You will see if the oil pressure match your problems if so then there is an internal leak or bad oil pump or old engine oil.

Hope it helps.

Can the truck be driven at all? I would never get the tranny oil replaced if the tranny is working ok. Quite often when this pocedure is done the problems start. All you have to do is pull the tranny dipstick and smell the oil on the stick. If the oil smells burnt, that is a good indication of problems. If not and the truck can be driven I would be going somewhere else. I had a 2002 Yukon that needed an engine. Used engine with 40,000 Klics at an auto recycle shop was 800 bucks. $300 to get it installed including A/C charging. How much does the shop want to rebuild the trans.? Better not be more than my engine replacement anyway call around and get some opinions and advice. Good luck

ur oil sending sensor is bad it reeds the oil pressure

If there is an erratic movement like that, it would seem that your sender wire is loose or damaged, or your sender is bad. Normally pressure fluctuations will not be fast enough to produce the readings you describe.
These gauges are not really what can be called gauges anyway, as I found out in my 93 F250. They just take a reading at the sender, and if it is within a range anywhere within normal specs, which run something like 4LB to 80LB, the gauge will just stay in the middle of the normal range. What I heard was that there were too many customer complaints about the needle moving all the time, so they replaced it with one that would stay right in the middle which would be acceptable to most all drivers.