Engine loses power

Most likely cause is the generator. They develop huge voltage spikes that destroy the internal diodes and voltage regulator and they interfere with the computer sensor signals. With one bad diode of the six you will only be able to get exactly one third of the rated current and that's not enough to meet the demands of the electrical system under all conditions. It is common to go through four to six replacement generators in the life of the vehicle. To reduce the number of repeat failures, replace the battery at the same time unless it is less than about two years old. As they age they lose their ability to dampen and absorb those spikes.

This guide can help

https://www.2carpros.com/articles/engine-has-low-power-output

Please run down this guide and report back.

Sounds like a plugged exhaust. Easy to run a pressure test on it.

Could also be a plugged fuel filter.

Have the fuel pressure checked. You could have a clogged fuel filter affecting the fuel supply resulting in loss of performance.

If the Malfunction Indicator Light is shoiwng, get a scan to cehck for trouble codes.

What is the trouble code?

Basics have been covered so you need to go further into diagnostics.
Have you checked the fuel pressure and air filter?
Try cleaning the MAF.

Have you checked for vacuum leaks? Also, even though the fuel pump is 3 years old, you may want to check fuel pump pressure at the fuel rail. You could have too little or a bad regulator and too much.

Let me know.

Joe

How is it losing power? Electrical or engine power?

If it's engine power does it rev freely when you shift to neutral? Does the exhaust note sound the same?
With it in gear and you step on the throttle what does it do?

It could be many things depending on what your answers are.

Could be one of the following below that's causing it

Oxygen sensor
Catalytic converter
Dirty fuel injectors (cleaning the injectors often fixes this).
Bad MAP (manifold absolute pressure) sensor
Bad TPS (throttle position) sensor
Bad or dirty MAF (mass airflow) sensor
Low fuel pressure (leaky fuel pressure regulator or weak fuel pump)
Vacuum leaks (intake manifold, vacuum hoses, throttle body, EGR valve)
Bad gasoline (fuel contaminated with water or too much alcohol)

Sometimes, what feels like a hesitation is actually ignition misfire rather than lean misfire. The causes of ignition misfire may include:

Dirty or worn spark plugs
Bad plug wires
Weak ignition coil
Wet plug wires

Scan for codes and check fuel pressure then check vacuum at idle if 15" or below suspect clogged converter.

Is the check engine light coming on at all? If not, then it sounds like the transmission may be slipping.