how to replace the speed sensor? on 1997 Chevrolet Astro

the van only goes 20mph even when your foot is on the gas pedel,

Asked by for the 1997 Chevrolet Astro
Agree with Roy, clogged Cat Converter or insufficient fuel pressure or fuel pump volume!
1 more answer
sounds like a clogged cat converter. go to a shop and have it checked.