I would start by replacing the fuel filter.If that does not help have the exhaust checked for any back pressure.Most exhaust shops will check that for free.
I will try the fuel filter first. Where is that located on the engine?
It is located on the frame rail on the drivers side.
I found it, replaced it, took van out for a spin, and filled the gas tank. Fuel on the intake side of fuel filter was brown, clear on the outtake. Engine idles and runs rough, but there is more power than before. Engine shimmy when transmission shift at about 35 mph.
You will need to check the exhaust for any back pressure and also see if you have any computor codes.