Hi, reading Grizzlys thread on a similar problem, I have to agree it sounds like an air/fuel ratio problem. Grizzly, did you try replacing your intake manifold gaskets? Try holding the engine at 1500 RPM and spray some carb cleaner around the edges of intake manifold. Does the RPM increase? If so the gaskets are bad. Have you tried clamping the Pvc and booster hoses with vise grips and driving it? Just trying to eliminate any possible vacuum leaks that might affect the air/fuel ratio. Also, I would buy a fuel pressure guage and splice it in the fuel pump to carburator line and run enough hose so you can read it while driving. It would be helpfull to eliminate a fuel pressure problem. Could it be a worn cam eccentric? I would also get a vacuum guage and hook it to a good intake vacuum source. Is the vacuum reading steady or is the needle bouncing around which could indicate bad intake gaskets. Run enough hose so that you can read it while driving. We need to know what the fuel pressure and vacuun readings are doing when the bog occurs.
Is your truck an auto or manual trans?
I am confident with some good diagnostic techniques your problem can be solved. Grizzlys problem, too.