97 chev asto 80-90 knh shift

My van seems to run extremly rough only around 80-90 KM. If i step on the gas it is fine. There also is an ordour, not gas but similar to exhaust smell. It would almost seem as if trying to stall, jumpy like.

Any suggestions

a bit more information about your problem might help. Year model, engine, recent maintenance, a little more description of the odor.
My lower conversion skills are stunted at the moment, but I think 80-90 kmh is about 45 - 50 mph yes? Just about the speed the overdrive kicks in?

The Van is a 4.3 Vortex 2 wheel drive, Yes that is about right 80KM- 90 is Appox 50-55 MPH.
Oudor al,ost smell like exhaust, not sure where it is coming from
No Maintence redecntly exept back wheel cylinder

The first thing I think I'd do is check the exhaust system for holes. Touch every part that you can't see with your hands. A leaky exhaust is hazardous to your health.
You may have a partially blocked catalytic converter.

Hmmm...
One other thought. Check the EGR valve. An EGR gunked up with carbon will cause rough running. And If the gasket on the EGR is mush, you might be experiencing some exhaust leakage there.