Missing out around 1500rpms

I have a 2000 Impala with a 3.8 and about 105k,when you drive,you can feel a miss in the engine.At first I thought it was a TPS,so I replaced it.It didnt help,took it off an put the old one back on.Let the car warm up,put a timing light on the sparkplugs and ran it up to about 1500 rpm.I have a misfire.The misfire is on all the plugs.So,Is it the computer or Crank Shaft Sensor??Or could it be something else Im overlooking??

Many things can cause this lean mixture, maf sensor, ign module to name a few, a full scan would be the next step.

Its not really a missfire,its not getting spark at times.I just dont want to take it to the dealership and have them tell me its going to be $200 dollars just to look at it.