My 2002 chevy blazer has been having these DTC codes for a while now and I've had my truck diagnosed a few times and I've replaced numerous parts but the codes are still coming up.

I've replaced the O2 sensors, the fuel pump, the fuel filter, the ignition coil, the distributor cap and rotor, the spark plugs and wires, the spider injector, and I also replaced the intake manifold gaskets after being told my intake was leaking coolant.

Everything I replaced was diagnosed bad so I haven't been needlessly throwing my money away. I'm just confused at why my truck is still running in a rich condition.

We had just replaced the intake manifold gaskets yesterday and while driving out today the P0128, P0172, and P0175 codes showed up again, plus one I havent seen before, P0327(Knock Sensor Problem?). Which mean Coolant Thermostat (Coolant Temperature Below Thermostat Regulating Temperature) and System Too Rich Banks 1 and 2.

Does the code P0128 mean I need to replace my thermostat, and would a bad thermostat be causing the rich condition and/or the P0172 and P0175 codes to come up? Or would a faulty coolant temperature (ECT) sensor or intake air temperature (IAT) sensor be the problem?

I appreciate any advice and help, thank you.