My sister has a 98 fullsize chevy van. It has the 350 engine. The thing seems to chugg realy bad once you hit 45mph. No one can find out what it is. They have replaced all the plugs...coil. wires.. And the oxygen sensors. Still doing it. Anyone have any ideas?

Hey,
I had the same problem with my chevy van, and the problem was not enough oil in the automatic gearbox... if your van is automatic check it...