I was going threw the exact same issues and what it ended up being was when GM flushed my fuel system and cleaned my Throttle body the took all the sensors off and the idiot didnt put the TPS back in correctly and wow car ran like **** for ages. I took it off and when I reinstalled it you have to make sure the little arm on the tps sits under the arm on the part thats in the throttle body. Woke the car up, No more bogging But now I have a TPS for sale and Maf sensor that I bought for nothing thats to GM. Make an offer if anyone needs a MAf etc Its brand new and it is a Ac delco.