Ever get a full tune up this decade? yes/no.
no , then what are you waiting for, some guy to charge you for new engine with only bad spark plugs>? or fuel filter? or air filter?
which engine, be the first in 100s to say.
most dont and expect helpers to be like god, clairvoyant.
or super man with 12,000 mile xray eyes, really?

2004 has 6ve1 V6 but not in a 2001.!
2004 last isuzu car here. became rebadged cars. GM
but the 2001 i think is a Rodeo, so says the wiki!

If the gas foot causes engine RPM to raise super high over 3000 rpm and not attendant car speed increase(mph)this is called transmission slip. is it slipping , no? then its a weak engine
easy no ?
we dont have these parts in USA>????? change pluck and tortle mouth if fact , perplexing to read....

weak engines> facts. all.
reduced power has any causes, over 50, so will not cause you to go broke with my silly wild guessing as seen here. every day.

the engine power can drop from 3 reasons.
besides a bad engine, 25 reasons there.
in physics they are, (a good engine with full compression tests ok)

1. lack of fuel (low fuel pressure)
2. too much fuel, flooding misfire.
3. and huge list of causes of misfires
4. lost power misfiring is violent and engine shakes. (bad spark?)
5. lost power feels only like dragging weight we call bogging.
6. and is usually fuel pressure loss. or weak injections.
7. bad sensor to the PCM , scan the PCM and win.
8. lots more, but no thesis today, just a short list.