hello, New to this forum. i got 91 silverado 1500 with 5.7 issue im having is the engine stumbles a little whenever it is in R or D. At idle in Park or N the engine runs smooth no signs of hesitation. No code and /or light on. First found IAC valve getting stuck replaced it. issue got better but still there. checked MAp-ok Knock sensor-ok 02 sensor-new with a nice wavefor at idle. temp sensor-new, TPS- ok smooth wake form, new plugs and cap n rotor..... ONe thing i notice is that when i spray brake cleanner in the intake manifold gasket area, the 02 tends to pick up that extra fuel that i'am sprying. Any ideas or commomng problems anyone has gone through?? Thank you.