Stutters at full throttle, ?????HELP

[429mustang]

The questions actually for my other car, my astrovan with a 355 smallblock, but I figured maybe someone would have an idea. When I floor it and start to take off it goes but way slower than usual and starts spuddering (sounds likethumping/ backfiring). I don't understand cause the plugs still look good after driving like this for almost a week. It's slow as sh*t now, I took apart the carb (edelbrock 600) and reset the floats and checked the plugs/distributor and nothing seems out of the ordinary. Anyone have any ideas? The fuel filter/lines are clear, and also, my oil pressure shows it's usually around 20 then drops to 0 when I slow down, the oil is full and I tried replacing the sending unit and still the same. I know it's a chevy, but any other ideas would be really appreciated.