Ok I have a 2002 Chevy Blazer 4x4 with the 4.3 liter V-6 vortec and auto trans.
When I'm not driving it hard like towing or hard acceleration at speeds above 45 mph it is fine.
But if I'm towing or accelerating above 45 mph real hard the check engine light will start flashing and it loses power.
I have a code reader and multiple codes show up.
Both cylinder banks 1 and 2 running lean.
Mass air flow sensor performance issue.
Multiple cylinder misfire.

Within the last 2 years I have replaced the spark plugs/wires, rotor and cap. mass air flow sensor, coolant temp sensor/wire, crank sensor, PCM, PCV valve and fuel filter.

I have been told possibly it could be the EGR valve, Spider fuel injector unit or intake manifold gasket.

If it is the spider fuel injector unit any suggestions on the best replacement unit to buy?
I have looked on Amazon and eBay and the reviews on spider fuel injector units for sale to order are generally bad.
I called my local GM dealer, and they told me GM stopped making OEM GM brand replacement spider fuel injector units.

I haven't seen enough diagnosis happen yet to condemn anything.

What are all of the codes?

What is the fuel pressure?

You got codes but don't share them. Are you wanting help fixing or suggestions as to what to replace?