My 1984 Toyota Pickup 4WD with the cabureted 22r.

My 1984 toyota pickup 4wd with the cabureted 22r 2.4l 4 cylinder engine will start, run, and idle fine. The problem is that when the engine reaches a certain load threshold it stalls. This happens while on the road at speeds that vary depending on conditions, but usually around 45-60 MPH. In order to fix this issue I have replaced the fuel pump, the fuel filter, all vacuum hoses, the carburetor, the radiator, the ignition control module, the catalytic converter, the ignition coil, and the power steering pump. I have tested the pressure on the EGR valve and the EGR vacuum modulator, tested the distributor diaphragm, and performed a complete tune-up including new plugs, wires, distributor cap, rotor and timing.

I am at a loss as to why this vehicle would still be stalling while driving when it reaches a certain load threshold, and have no idea where to go from here.