I don't know if this is related but...
I have a 3.8L Lumina that occasionally shudders when I step on the gas, after putting it in gear. It doesn't happen regularly -- just out of the blue, for no reason, when I'm doing a lot of delivery driving.
What happens is I'll start the car, shift into drive, step on the gas and the car won't move forward much, but instead the engine shudder violently and make some ungodly noises. The only thing I can compare the shudder to is when I once accidentally put spark plug wires in the on the wrong plugs, screwing up the firing sequence(on a different car though). This shudder lasts 1-2 seconds and then the car runs fine.
I think the car may have done this once before I shifted into drive, which makes me believe it may not be the tranny. It may be just wishful thinking though.
I have a constant service engine light on because of some gas fume evaporation system malfunction that I don't really care enough about to fix right now(yes, I've changed the gas cap and it is tight), so I don't know if there were any new codes sent.
Could this be the crankshaft position sensor or an intermittently bad injector? Or is it a solenoid not putting the car into gear in time before I accelerate(I've been waiting a few seconds after shifting into drive and it hasn't happened since)?