Po 171 po 174 98 Blazer

P0171= Fuel trim lean-bank 1. P0174=Fuel trim lean-bank2.

This means your air/fuel ratio is lean and the computer is attempting to compensate but can't. Because it's in both cylinder banks, I doubt if the sensors are bad. Look for a common problem. (The reason the codes won't go away is the problem hasn't been fixed)

Look for vacuum leaks first. You said "new injector module, fuel pressure." Did you mean new fuel pump or pressure regulator? And the injectors are controlled by the computer. Did you replace that?