[rgunlock]

Sounds like the OP got it figured out for his truck, but I was having similar symptoms in my '78. Wasn't generally a problem, but put me on the side of the road several times when going up steep grades on a long road trip.

In my case, when I swapped in a crate 350 I also replaced all the rubber portions of the fuel line. There was a fairly sharp bend in the hose coming off the steel line on the frame rail to the mechanical fuel pump. Normally, the hose stayed open. In this case, I believe heat softened the hose to the point that it was pinched. As long as I held a steady speed it was fine but when I needed more from the engine accelerating or climbing a grade it would darn near die on me.

Before I discovered that this was the culprit, I too had blamed fuel filters and replaced them. Blamed the pump when that didn't work and replaced it. Had the carb apart a couple times. Added a 1 inch spacer between the intake and QJet - none of which helped. Hopefully this will help someone else that runs into fuel starvation symptoms.