I have returning p0401 code i have cleaned passage and repla.ced the egr valve

first of all you need to verify inputs to the egr, do you have good vacuum? when you activate the egr = does the engine stumble or stall? I have seen a few map sensors affect egr systems and codes. Gm has some reprograms for this system as well. Dont forget to measure exhaust pressure as well as that could set this code. Hope this helps