Did it just start doing it when the weather warmed up? A lot of these trucks seem to have vapor lock issues when using/running a metal fuel line up to the carb. How dirty was the fuel filter? When I replace one, I tap the inlet end against a block of wood to see what comes out. Before I replaced the old gas tank in my 109, it was so rusty I was replacing a fuel filter every hundred miles! But if you already changed it, that's likely not it.
Will it rev up nicely after stalling, if you take it out of gear? If yes, then it's not getting enough fuel from the line under load. That could be a bad/weak pump, old fuel lines that are collapsing under load, or a blockage in a line, at the carb, or the tank itself.
61 II 109" Pickup (Restomod, 350 small block, TR4050)
66 IIA 88" Station Wagon (sold)
66 IIA 109" Pickup (Restomod, 5MGE, R380)
67 IIA 109" NADA Wagon (sold)
88, 2.5TD 110 RHD non-hicap pickup
-I used to know everything there was to know about Land Rovers; then I joined the RN Bulletin Board.