Hi, welcome to JustAnswer!. This is Ed.
Oooof.... and I mean oooof. You have engine damage.
For the spark plug you found to be physically deformed and have the horrible low-speed driveability you have, you almost have to have a valve hanging open. It could be a broken valve spring, a dropped valve seat or some sort of outside debris that made its way into the combustion chamber of AT LEAST that one particular hole. It's not possible to say just what happened yet, but I can't imagine a broken spring causing both the loss of driveability and the broken spark plug.
You have debris circulating.
That's going to bring us back to a dropped valve seat or something introduced to the engine from above. If there has been nothing done to the engine within thousands of miles before this event, I'd have to place odds on the dropped seat theory.
Your 3.9 uses aluminum cylinder heads, which requires the use of pressed-in hardened valve seats. Overheating of the engine is a major contributor to a dropped seat because it expands the aluminum and loosens its grip on the seat, but sometimes stuff just happens. When a seat drops out, it's immediately munched up by valve action and piston interference, which would account for your destroyed spark plug. Check your compression on at least cylinder #2 and if bad, run a test on the remainder of the engine.
Chances are good that you'll be pulling that cylinder head at the least.