I think you're wrong.

The torque converter is supposed to slip to allow the engine to idle without stalling. I have never seen one fail to do this, and I can't think of a way a torque converter could fail and not do this. I know of a few ways a torque converter can fail and not transmit torque to the transmission, but then the truck acts like it is in nuetral all the time.

I think there is something wrong with the engine that prevents it from idling with some load on it. A vacuum leak can do this, a carb problem, wrong timing, low idle speed, etc.