Have you checked the fuel level in the float bowl after it bucks and dies I had a truck that did something similar and it idled and revved up fine but when I would drive it under higher loads it would buck and die and it ended up being partially plugged fuel lines
It might be the accelerator pump if it sputters and almost dies on acceleration
It is definitely a weird situation. 84toyota4x4sr5 is right, check the fuel level in the sight glass as well it should only be half full, also blow out the fuel lines and check the fuel filter it could be clogged up so it is starving the engine of fuel. Have you checked the fuel tank? It could be dirty in there and is just clogging up the filter. That is what happened to mine it was full of sand
