05 trail Blazer

Of coarse I have done all of that, and changed both o2 censors. Also replace the fuel modulator. ( Fuel pump in the gas tank very expensive) all of this made it better but never truley went away. The low idel/studder was obviouse befor doing it, but only I could notice right after I did these things, but now is progressivly getting worse. It mainly happens when you reve engine, and than let off the gas. The rpm dips way down, and then plains off. Cleaning the throttle body also did not work