My '06 SVM just turned 100k. At 99k it suddenly developed this misfiring problem...
I did a routine throttle body cleanup and that helped a little..
So I checked the plugs and wires..
With the lights off in the garage I could clearly see that the #4 wire (long wire) is leaking voltage..
Which sux since they only have 40k on them.
I pulled the plugs and they looked ok but I found the gap had opened up to .050 on every one of them so I backed them back down to .039
That helped alot...the sputter is down to a random stumble. Mostly when under load, like accellerating from 40 in 4th gear. I'm guessing that glowing wire is the culprit.