Help with P0171 code

P0171 is a "System too lean" error code. This is caused by the engine receiving more air than fuel so it compensates by adding more fuel (hence positive LTFT and STFT). A common way to diagnose problems with P0171 is by checking short term fuel trim (STFT) at idle and at around 2500 RPM. If the STFT is a positive value at idle and goes back down towards 0 at 2500 RPM it indicates a vacuum leak somewhere between the MAF and cylinders (due to high RPM creating a strong vacuum making any leaks insignificant). If the STFT stays the same at both RPMs then the problem is likely an issue with the fuel delivery system, not a vacuum leak. I believe this is your case as you mentioned these values at highway speeds. Since your fuel filter has been changed I would recommend also checking the fuel injectors as they might be starting to get clogged.

EDIT: I just took a look at your excel sheet you posted in the comments. I noticed that as your RPM goes up towards 2000 the STFT goes from 46 to 0. This is a definite sign of a vacuum leak as mentioned above. There might be a little hole anywhere after the MAF. You should look for tears or fractures on any intake component leading to the cylinders. A small hose may have came loose or has deteriorated due to heat and is leaking. I recommend searching for techniques for findings leaks as finding it can be quite challenging. Otherwise it is quite safe to drive as the issue disappears during normal driving (only occurs at idle), only your fuel consumption might suffer slightly.