Why does my engine bog down when I press on the gas pedal and then rev up and then backfire through the carb?

I have a 92 dodge B350 van 5.9. I have to feather the pedal to get it up to speed. If I hold the pedal down for a few seconds it will bog down and then backfire through carburetor. I tried adjusting the timing by moving the distributor to the left and right didnt fix problem. If I am going up hill it will barely accelerate. After driving for 20 minutes or so if I have to stop at a light or stop sign I can barely get back up to speed. I changed the fuel filter near the gas tank and it ran good for 2-3 minutes then it started doing the same thing again. I don't hear any vacuum lines leaking. The 2 injectors appear to be working fine. I sprayed carb cleaner in carb while holding the pedal and it maintained the rev until I stopped spraying. As if it was not getting enough fuel into the carb before I sprayed the cleaner. But when Idling the engine sounds fine.