Greetings!
you mention changing a lot of engine sensors, but make no mention of what any of the voltage readings from them are/ were, or what codes you may have retrieved from memory (also, knowing whether they are KOER generated or KOEO codes can be useful information).
Teh most,likely failures to produce the symptoms you describe would be a resistance fault in the coolant temperature sensor circuit, or a restricted catalytic converter.
If the CTS sensor circuit has high resistance or is shorted to ground someplace, it will result in the powertrain control module calculating spark advance and injector pulsewidth incorrectly, resulting in poor performance and lack of power.
If the exhaust system is restricted due to a degraded Catalytic converter, the engine will have no power and fuel economy will be terrible.
Use a vacuum gauge to check engine vacuum; a restricted exhaust flow will cause engine vacuum to read low (normal is around 21 in/hg at steady cruising speed); if severly restricted it will drop near zero at higher engine speeds. Also, shake the exhaust and listen for the sound of broken ceramic rattling around inside. One final test would be to loosen the exhaust pipe connections at the manifolds and test drive the vehicle to see if power is greatly increased.
I hope this is helpful; if so, an accept would be most appreciated! thanks!
