Troubleshooting low engine power uphills

my 02 Corolla (230k miles) has low power, especially uphills. I did a vacuum test and fuel pressure test, as I was suspecting a clogged exhaust or a faulty fuel pump.

Both readings are normal, except that when the electrical fan turns on, the vacuum drops a bit (2-3 mHg, remains within specs) and the fuel pressure fluctuates very rapidly (the needle shakes). Can I make any conclusions based on these observations, or should I be testing something else to understand why I have low power uphills?

Thank you for your help!