Hello!
With the symptom you describe, the first things that come to mind are restrcted fuel delivery, or a blocked exhaust system.
You have replaced the fuel pump, but do not mention having replaced the fuel filter. You may want to check for a clogged fuel filter before doing anything else.
An exhaust restriction may be present due to a degraded catalytic converter. If the inside of the converter comes apart, chunks of the internal ceramic can shift to the back of the shell, blocking exhaust flow. This will cause symptoms just like you describe.
Youc an do a quick easy test for an exhaust restriction by connecting a vacuum gauge to the intake manifold and then opening the throttle. A normally running engine will show about 18 to 20 in/hg vacuum; when the throttle is opened the level will drop momentarily and then recover as the engine accelerates. An engine with an exhaust restriction will not recover... the vacuum reading will drop toward zero and stay there during acceleration.
You can also loosen the exhaust pipe where it attaches to the manifold to see if power is restored.
ASE L1 Master Technician
25+ Years experience as a professional working automotive technician; ASE L1 master technician.