The problem with finding intermittent problems is the are intermittent (duh). In the case of my fuel pump problems it always checked out perfectly. It was only after I checked my fuel pressure under a full load when the problem finally surfaced. As I live out in the middle of nowhere I have ready access to roads where I can open it up to 100 mph or more. But for a city dweller it would be very hard to put their engine under a full load for more than several seconds and then only in a lower gear as the speed would become too great.
If you ever suspect your engine isn't putting out the amount of horsepower it used to you must check the output volume of your fuel pump to be sure it's delivering 1-1/2 pints in 30 seconds and at 5 psi. All stock fuel pumps put out 5 psi because the diaphragm return spring is calibrated for 5 psi but if your fuel pump has leaking valves the output and pressure can be low.