sounds like what a friend of mine's 98 K1500 Burb does. I can do it at a lot of speeds from 40-65 (what I tried it at) and it is pretty violent in my book. I suspect it is the converter itself, but hard to prove either way. If I apply the brake slightly to disable TCC, it never happens. So distinctly TCC related.
Try this, can you make it do it in 3rd gear? It will lockup in 3rd, see if it still does it.
Originally Posted by southmainmotors