2001 Chevy Monte Carlo

I have a monte carlo 2001 3.4 engine, the temp gauge does not work I have replace it and checked the circuit. Still nothing now the transmission is acting up the car wont shift past second gear or go over 40 mph the egr code is coming up along with maf sensor and cylinder 6 mis fire I have replaced wires plugs coil and the maf and the egr and pcv and much more with no fix I consider myself to be mechanically inclined so I am starting to think that the pcm is the cause of all these random problems and was wondering what you thought