Poor Engine Performance at Low RPMs?

I have the vehicle listed above GLS. A few weeks ago, I started experiencing poor engine performance. Nothing drastic, but not as it should be. It has since then been slowly getting worse to the point that without feathering the clutch more than I am comfortable with, I am struggling to get up hills that weren't previously an issue.

I have run fuel cleaner through the system, changed the spark plugs, changed the oil and oil filter, changed the transmission oil (a few months ago), and replaced the air filter. I also fixed a couple wires that a mouse had chewed through - a wire to the throttle body (unsure which connection the wire carries) and the wire to the oil pressure sensor. I also changed the oil pressure sensor after fixing the wire going to it, as the factory sensor was quite rusted, and the engine performance went back up to normal when I initially fixed the wire then got worse again.

When the engine's RPMs pick up to 4,000 or so, the engine begins performing as expected. It's almost as if proper torque cannot be generated at the lower engine speeds. The issue is also somewhat intermittent - it will be sluggish then start performing normally for a couple minutes then go back, though it has mostly been performing poorly and slowly getting worse over the past 3 weeks or so.