How old is the fuel pressure regulator and what are the numbers on it? You said the plugs showed rich.

Does the car start up when cold, quickly on it first try of the day? What I mean is no long cranking moments. I am thinking its rich enough to start ok but the engine is a lot leaner after it warms up.

When was the last timing belt change or the last time you loosened the tensioner bolt and retightened it? I wonder it the timing is off (a smidgen) almost a tooth.
The combination of it with a lsticky spring onto the diaphragm in the FPR just might get its act together on the hills and pulling.
The spring has to close down on the return line going back to the tank while accelerating or pulling a grade when there is less vacuum to hold the line open.

The rich plugs are saying something is not right or the O2 sensor should be yelling at the ECU.

I cannot get it to add together without more symptoms.

What's your gas mileage? Stick or automatic transmission?
Give us a few more quirks or past history.
Phil