Engine misfiring and losing power?

Inspect and test the airflow meter and throttle position sensor-

The VSS is located on the speedometer assembly

With that many miles, and not having the complete history, I can only give you suggestions. No, it is not time you swap to another engine, just yet. My 95 GA16 has 240K, and it runs better than most Sentras out there.

First thing that I would do is a compression test. It will show which cylinder is not operating properly. It one of them is way below spec, then you may want to consider the engine swap, or just rebuild that motor.

If the compression test is good, check your ignition timing. It should be 8 degrees BTDC. Make sure that you don't have that much play on the distributor shaft. Test your coil. You have replace everything (tune up wise, except the coil).

Test your fuel pressure at the fuel rail.

You also mentioned that it happens in cold weather. Check your coolant temp sensor.

Lack of acceleration, chugging, hesitating, bogging, misfiring etc. Could be caused by one of the following below:

Inspect and test all the items below-we start here and comeback with the results.

Oxygen sensor.
Catalytic converter.
Fuel injectors dirty/sticking.
Mass airflow sensor/Airflow meter.
Throttle position sensor.
Crankshaft position sensor
Knock sensor
Manifold absolute pressure sensor.
EGR Valve
Fuel pressure regulator leaking or defective fuel pump.
False air leakage.
Fuel contamination.
Foul/defective spark plugs.
Open spark plug wires.
Ignition coil/Coil packs defective.
Incorrect ignition timing.
Cap and rotor.

Note:If it doesn't apply disregard it.

You probably showered the TPS and MAF sensor connectors causing the problem.

Tune up and a fuel injection service

Probably all of it. Requires changing Spark Plugs, Air Filter, Oil Change, etc. Fuel injection service can be a little bit more of a challenge.