Tom...I just had to answer your suggestion...my husband owns an S-10 (only 4 cylinders though) and we tried that. The stubs moved a bit, I heard some roots cracking, but in the end, his engine started smoking!! So, rather than destroy his truck, we gave up. I suppose if he had had a more powerful truck, it might have worked.
I think I'm going to have to do some more digging and use an axe on them, or wait until a landscaping company calls me back. Thanks though!!