just bought a 2000 silverado 5.3 ext cab 2wd. kinda ran a bit rough so i changed plugs and wires which didnt help at all. then pcv and fuel filter. just does it in gear and idling in park is like the engine is shuddering. any ideas? im thinkin somethin with iac, tps or o2 sensor?[:@]

 

it may be idling too low...there is a re-flash to fix that,usually

 

idles at 500 rpm when warmed up in gear, park is maybe 50 rpm higher. re-flash is that a pcm reprogram?

 

If your truck's mileage is getting up there you may wan to clean the MAF sensor. As they get dirty they are unable to detect airflow over them.
It worked on mine. Might as well descreen it while yourat it! lol( contact cleaner from Radio Shack )

Best of luck

 

They also sell MAF sensor cleaner at NAPA for this specific purpose.