I do not believe that those codes could be mechanical. P0171 and P0174 indicate system running lean. I would recommend checking for vacuum leaks, low fuel pressure, contaminated fuel/too much ethanol in fuel, or faulty mass air flow sensor.
I am posting some guides on basic checks for vacuum leaks and fuel pressure.
https://www.2carpros.com/articles/how-to-use-an-engine-vacuum-gauge
https://www.2carpros.com/articles/how-to-check-fuel-system-pressure-and-regulator
To check the mass air flow sensor your scan tool will need to be able to read live data. With engine warmed up and all loads off example: lights off, A/C off. You need to look at the mass air flow data in grams per second. The reading should be close to what your engine size is. You have a 2.8L engine. In theory your mass air flow should read 2.8 grams per second but you will most likely see something of a range of 2.3 - 3.2 grams per seconds. That is a rough estimate but if you post the readings we should be able to see if your within normal range.
If okay then take a fuel sample and see if the fuel is clear or cloudy. If cloudy then your fuel is bad and will cause lean running codes which could cause a misfire. Let us know those readings. If all looks good I will let you know another test for the mass air flow sensor when at cruising speeds. For that test you will need a co pilot to read the data off the scan tool.
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Friday, January 24th, 2020 AT 10:38 PM