WyoTransAm

Ive Got a 94 T/A bought it a year ago. SES light came on after buying it on way back home. tried to get a code read on it wont give out a code. figured it was probly a o2 sensor changed both out when i had the dual exuast done lights still on and losing power runnin a second slower than it should be running and sometimes has issues taking off from red lights wit occasionally spit and sputter. when started up light wont come on til the motor usualy revs to bout 3000 rpm or you downshift to slowdown for red lights. any ideas thinkin may be a spark plug but all wires are on tight