I apologize, when I first read your post I didn't catch it was in an RV/truck - hence my smoky burnout comment.
I'm not disputing what your mechanic told you. I have some diesel engines (so equipped) that run in much harsher environments than your RV and that reading would not send up red flags for ME. However, I can see your concern since that's what you mechanic told you.
To your original question, do these fail? I haven't seen that myself, but this is an imperfect world. I will say, they are a mass market item that rely on a constant pressure spring that is all the 'calibration' there is; so I can see where there might be some variance from one to another. The purpose of the minder is to keep you out of a catastrophic filter failure - not really as a diagnostic of the engine. You did exactly what a high reading on that minder would have you do - changed the filter.
Now, you have a new filter and you're right back where you started with same reading. Have you observed any indications you're starving for air? Reduced power on long pulls? Excessive black smoke? If the answers are yes and you have a new filter then I'd start looking for a rubber elbow somewhere in the intake line that might be collapsing under load, or some other restriction in the intake. (honestly, I'd think that would read higher on your tattletale) If the answer is no; everything is exactly like it was before - I would not be alarmed.
If you are really concerned - put a new on there for a few bucks, or just do it for comparison. My suspicion is you are okay. Happy Thanksgiving.
