I had a similar problem with mine. As irt turned out, it was the timing. Once it was advanced (15 degrees in my case) the popping and dying under a load want away. I'd suggest advancing it abou 5 degrres ant a time , until the engine sounds happy. You'll want to follow Toyvo's advice, too, as the RPM will increase with the advance, so the idle will have to be reset.
I recall from your other posts that you have a hydraulic cam, so that should eliminate valves, though you might check them just to be certain.
I should mention that my truck does not have a vacuum advance.
