Think about it- when you put any load on the car it dies, and it happens when you move or when you add a load. Sounds like a bad ground that is loose or damaged. As Jrichker suggested, get DVM and start doiing a volage drop across the primary circuit and then for continuity along the ground side. There are grounds from the battery to the block. another 2ndary ground for the EEC that goes to the post behind the battery on the firewall and to the neg battery terminal, another ground for the HEGO orange wire to the firewall, another ground wire from the firewall to the cylinder head or block behind the driver side, and if you have a 3g alternator there should be another ground cable from the block to the driver or passenger side frame or inner fender. All of these connections need to be tight, clean, shiny and free from dirt, grease, etc.