Can I trust that little gauge?????

Here is my experience with that "minder" I'm old school and visably check the filter from time to time. Well on my '95 Cummins, I thought well maybe it is legit. Coming back from Texas on I-59 near Birmingham, Alabama my wife was driving the '95, I was behind in the new 2003 Cummins pulling our trailer. About 5 miles from a Flying J she calls me on the radio and says she has no power, about 45 mph at best. We puled in at the J, fueled up and went to a near-by state park. Sat there that evening thinking about what could be the issue. The light came on in my head that I was relying on the "minder", maybe I better eyeball it myself. Well it looked like 100 miles of bad road. Next AM down to a nearby NAPA, got new filter and installed it. No power problem after that on the way back to PA., then on to Calif and AZ. I still have the '03 and filter gets eyeballed and every time I look at the "no-minder", it always shows good.