Chip, I had decided not to commment on your post, but I've been thinking about it and I have to say...
If your jackstands and the surface on which they sit are not strong/level/hard enough to support an idling vehicle, they are not adequate to work under.
We do things under our trucks that will impart more energy to the truck in more dangerous directions than a idling motor. I wouldn't get under the truck at all if I didn't trust the stands to hold it while it was running.
Joe
